95. The Primary formations are so called because they are the oldest known to us: they are not necessarily the first-formed aqueous deposits. Dr Hutton said truly: There is no trace of a beginning, and no signs of an end. In the Primary or Palæozoic (ancient-life) formations are found the earliest traces of life. The forms as a rule depart very widely from those with which we are acquainted now. The Laurentian rocks have yielded only one fossil—a large foraminifer named Eozoon Canadense. The Cambrian formation contains but few fossils—crustaceans, molluscs, zoophytes, and worm-tracks. The Silurian strata are often abundantly fossiliferous. All the great classes of invertebrates are represented, and fish remains also occur. The Devonian and Old Red Sandstone are also characterised by the presence of an abundant fauna. In the Old Red Sandstone are numerous fish remains; it appears to have been an estuarine or lacustrine deposit; the Devonian, on the other hand, was marine, like the Silurian and Cambrian. The Carboniferous formation is the chief repository of coal in Britain. It consists of terrestrial, fresh or brackish water, and marine deposits. The fauna and flora of the Permian, which is partly a marine and partly a fresh-water formation, are allied, upon the whole, to those of the Carboniferous, but offer at the same time many contrasts.
96. The Secondary or Mesozoic (middle-life) formations contain assemblages of fossils which do not depart so widely from analogous living forms as those belonging to Palæozoic times. The Triassic strata yield abundance of rock-salt. In Britain they contain very few fossils, but these are more abundant in the Triassic deposits of foreign countries. The oldest known mammals first appear in this formation. The Jurassic formation is very highly fossiliferous. It is distinguished by the occurrence of numerous reptilian remains. Nearly all the beds of this formation are marine, but there are associated with these the remains of a forest or old land surface, and a considerable accumulation of estuarine or fresh-water deposits; impure coals also occur in this formation. The Cretaceous strata are almost wholly marine, and chiefly of deep-water origin. But some land-plants are found, chiefly ferns, conifers, and cycads. Near the base of the formation occurs a great river deposit (Weald clay) with numerous remains of reptiles.
97. Among the oldest strata of the Tertiary or Cainozoic (recent-life) division we meet with the dawn of the existing state of the testaceous fauna—the Eocene (ēos, dawn, and kainos, recent) containing three and a half per cent. of recent species among its shells. The proportion of recent species increases in the Miocene (meion, less, and kainos, recent), although the majority of the molluscs entombed in that formation belong to extinct species. In the Pliocene (pleion, more, and kainos, recent), however, the extinct species are in a minority.
The Post-tertiary or Quaternary division comprises the concluding chapters of geological history. The Pleistocene (pleistos, most, and kainos, recent) contains no extinct species of shells, but a number of extinct mammalia. In the Recent deposits all the species of animals and plants are living. The Tertiary and Quaternary formations are partly of marine and partly of terrestrial and fresh-water origin. At the close of the Tertiary period the 'glacial epoch' of Pleistocene times began, and the British Islands and a large part of northern Europe and North America were then cased in snow and ice. Traces of glacial conditions have also been met with in the Eocene and Miocene. The evidence furnished by Palæozoic and Mesozoic formations points chiefly to mild, genial, and sometimes tropical conditions. But traces of ice action are occasionally noted (namely, in the Silurian, Old Red Sandstone, Carboniferous, Permian, and Cretaceous formations), pointing, perhaps, in some of the cases, to former alternations of cold and warm periods. Indeed, the belief is now gaining ground, that the so-called glacial epoch of Pleistocene times was not one long continuous age of ice, but rather consisted of an alternation of warm and cold periods. And it is not improbable, but highly likely, that similar alternations of climate have happened during every period of great eccentricity of the earth's orbit.
Section 1. What is Geology?
2. Define the term rock. How many classes of rock are there?
3, 4, 5. Into what groups are the mechanically formed rocks divided? Define the terms conglomerate, sandstone, and shale.
6. What is the nature of the rocks belonging to the Aërial or Eolian group?
7. Give an example of a chemically formed rock.
8. Give examples of organically derived rocks.
9. What kinds of rocks are embraced by the Metamorphic class?
10. What are igneous rocks?
12. What is the mineralogical composition of granite?
13. What is meant by a mineral?
14. Name five minerals which do not contain oxygen. Where does fluor-spar occur? What is the element that enters most largely into the composition of the earth's crust?
15. Name the forms under which the mineral quartz occurs. Name some of the oxides of iron. What is iron pyrites?
16. Name two sulphates. Name two carbonates. Name some of the silicates. In what kinds of rock is augite found? Where does it never occur? In what kinds of rock does hornblende usually occur? Mention three species of felspar. What is one of the most distinguishing characteristics of mica? Name three silicates of magnesia. Mention some of their distinguishing peculiarities. Where do zeolites commonly occur?
17. What is a quartzose conglomerate? What is a calcareous conglomerate?
18. What is grit? What is freestone? To what are the various colours of sandstone due? What is shale?
19. Name some typical Eolian rocks, and tell where they occur.
20. How do stalactites and stalagmites occur? What is siliceous sinter, and how does it occur? How does rock-salt occur?
21. Mention some of the varieties of limestone. What is cornstone? What is the composition of dolomite?
22. Name some of the varieties of coal.
23. What is quartzite?
24. Describe clay-slate.
25. Mention some altered limestones.
26. What are schists? Name and give the mineralogical composition of three schists.
27. What is the general character of metamorphic rocks?
28. How would you classify granite?
29. What is the mineralogical composition of syenite and diorite?
30. How do we distinguish the two groups into which igneous rocks are subdivided? What is meant by the terms amygdaloidal and porphyritic?
31. Name some rocks that belong to the acidic group. What is quartz-porphyry?
32. Give examples of augitic igneous rocks. Name a hornblendic igneous rock.
33. What are fragmental igneous rocks? What is the difference between trappean breccia and trappean conglomerate?
34. What is meant by the terms stratum, strata, and stratified? What is the difference between lamination and bedding? What is a section?
35. What is false bedding?
36. Briefly describe the general appearance of mud-cracks and rain-prints, and say how these have been formed.
37. What is meant by a succession of strata?
38. Which kinds of stratified rocks generally have the greatest extension?
39. How do beds terminate?
40. How may planes of bedding sometimes indicate a break in the succession of strata?
41. What is the nature of joints? What are master-joints, and what is their probable cause?
42. What is cleavage, and what is its effect upon the bedding of rocks?
43. What is foliation?
44. Give examples of concretionary rocks. What is the nature of chert and flint nodules?
45. Define the terms dip and strike. What is the crop of a bed? What are anticlines and synclines?
46. What is meant by an inversion of strata?
47. How does contemporaneous erosion indicate a pause in the deposition of a series of strata?
48. What is meant by unconformability? How does unconformability prove a lapse of time between the accumulation of the underlying and overlying strata?
49. What is overlap?
50. What is a fault? What is hade? How are the strata affected on either side of a fault? What is the appearance called slickensides? Under what circumstances should we term a fault a downthrow? and when should we term it an upcast? How is the approximate age of a fault sometimes shewn?
51. What are metamorphic rocks, and what is their general appearance? In what districts of the British Islands are they most abundantly developed? What are some of the appearances relied upon for distinguishing metamorphic from igneous granite?
52. How do igneous rocks occur? Define what is meant by contemporaneous and subsequent or intrusive igneous rocks. How does a contemporaneous igneous rock affect the beds upon which it rests? What is the character of the bed overlying a contemporaneous rock? What is the general structure of a contemporaneous igneous rock? What is meant by vesicular structure? What is the general texture of a contemporaneous igneous rock? What is the nature of the jointing in igneous rocks? What is wacké?
53. What is the nature of the beds of breccia, conglomerate, ash, and tuff, with which contemporaneous igneous rocks are often associated? What is a neck of volcanic agglomerate? How are the strata affected at their junction with a 'neck'?
54. How do intrusive igneous rocks occur? How do intrusive sheets occur? What effect have they produced upon the strata above and below them? What is a dyke? What relation do they occasionally bear to sheets of igneous rock? What is a neck of intrusive igneous rock, and how have the strata surrounding it been affected?
55. Mention some of the contrasts between intrusive and contemporaneous igneous rocks. What alteration is produced upon coal with which an intrusive sheet has come in contact?
56. What are mineral veins? What is the nature of the quartz veins in granite? How are the minerals usually arranged in the great metalliferous veins? What is a pipe-vein?
57. What are the great geological agents of change?
58. What is meant by weathering? How are rocks affected at the surface in tropical countries? What chemical effect has the atmosphere on calcareous rocks? How is soil formed? How are sand dunes formed? Mention some effects of the transporting power of the atmosphere.
59. Mention some of the chemical effects of interstitial water. What is the origin of travertine or calcareous tufa?
60. How have stalactites and stalagmites been formed? Give some instances of the solvent power of springs.
61. How are caves in limestone formed? Describe some of the appearances of a country composed of calcareous rocks. Describe briefly how a river erodes its channel.
62. Describe the geological action of rain.
63. What do chemical analyses of river-water prove? Give an example. What are pot-holes? Give an example of the erosive power of running water. What amount of mud is carried in suspension by the Mississippi, and discharged annually into the sea? What estimate has been formed of the total amount of mineral matter annually transported by that river?
64. What is alluvium? How is it formed? and mention some examples of its occurrence.
65. How is sediment deposited by a river in a lake?
66. What is the difference between lacustrine and fluvio-marine deposits? What is a delta?
67. Describe the geological action of frost. Describe the geological action of river-ice.
68. What are glaciers? What thickness do they attain in the Alps? What is their rate of motion? What are crevasses, and how do they originate? What are superficial moraines? What are terminal moraines? What changes does a glacier effect upon its bed, and how are these modifications produced? What is the character of a glacial river? What is the origin of icebergs? How is the general absence of blocks and stones in Greenland icebergs to be explained? What is the nature of a submarine terminal moraine? What is the ice-foot? What is the chief agent in distributing erratic stones and blocks over the sea-bottom? What effect upon the sea-bed must stranding icebergs produce?
69. What are some of the chemical compounds held in solution in sea-water? Which of these go to form the shells and skeletons of marine animals?
70. Describe the action of breakers on a sea-coast. How does frost aid the wasting action of breakers? What effect has the nature of the rocks in the production of inequalities in a coast-line? Upon what part of the sea-bottom does the material derived by the action of the breakers chiefly accumulate? What effect have the tides and ocean currents in the distribution of sediment?
71. What is the general rule as regards fine-grained and coarse-grained deposits? Mention a partial exception to this rule. What effect have tidal currents in shallow seas?
72. How are rocks disintegrated through the action of plants? What is peat? What may be inferred from the occurrence of shell-marl underneath peat? What does the appearance of roots and trunks of trees, and of remains of land animals under peat, indicate?
73. What, generally, is the geological action of animal life?
74. What is coral? What is a fringing reef? What is the general character of a barrier reef? Give an example of one. What is an atoll? What is the nature of coral rock? What is Mr Darwin's theory of the formation of coral reefs?
75. What is the nature of the Atlantic ooze? In what respects may it eventually come to resemble chalk and limestone? Mention an instance of the abundant occurrence in the sea of animalcules with siliceous coverings and skeletons. What is the nature of the red clay found at great depths in the Atlantic and Southern Oceans?
76. What are some of the notions held in regard to the internal condition of the earth? At what (average) rate does the temperature of the earth's crust increase as we descend from the surface?
77. What is the nature of the movements to which the earth's crust is subjected?
78. Describe the hypotheses advanced to account for earthquakes. Mention some of the effects of earthquakes—1st, as regards alterations of level; and 2d, as regards modifications of the surface.
79. Mention a good example of tranquil elevation and depression of the earth's crust. Mention some of the proofs of an elevatory movement. Give proofs that shew depression of the land. How may certain former changes of sea-level be accounted for without inferring any movement of the land?
80. What effect must depression have upon the strata forming the earth's crust? What is the result of a movement of elevation? What is the cause of cleavage?
81. What is the nature of the materials thrown out during volcanic eruptions? What is the general structure of a volcanic cone? How does molten rock make its escape from the orifice of eruption? What is the meaning of the terms lapillo, puzzolana, and ceneri?
82. What is lava? Describe the general appearance and mode of progression of a stream of lava. What effect is produced upon fragments of rock caught up and inclosed in lava; and what changes are caused in the pavement upon which it cools? How does a lava stream entering a lake or the sea behave in regard to the sediment gathering therein? To what is the basaltic structure due? How are the axes of the prisms in a columnar igneous rock arranged? Name some of the varieties of lava. What is the origin of the vesicular structure in igneous rocks? What portions of a bed of lava are most frequently scoriaceous? In what kinds of lava is the vesicular structure most abundantly met with? How have the vesicles become flattened? In what manner have they been filled with mineral matter? What is the origin of the dykes of modern volcanic districts?
83. How is metamorphism on the large scale supposed to have been induced? How may granite be at one and the same time a metamorphic and igneous rock?
84. Mention some of the views held with regard to the origin of mineral veins.
85. What is denudation? How do inclined strata prove that the strata have been denuded? How do faults afford proof of denudation? What have been the general effects produced by denudation on the face of the land?
86. What part have the subterranean forces acted in the formation of mountains? To what geological action is the present aspect of these mountains due? What has determined the direction of river valleys? How have the valleys, dells, &c. been formed? What effect have faults had in determining the direction of river valleys? What is supposed to be the origin of the deep rock-basins occupied by many fresh-water lakes? How is the waste of land by denudation compensated?
87. What are fossils? What is meant by petrifaction? In what kind of rocks do fossils occur most abundantly, and in the best state of preservation? and what reason can be given for this?
88. How do fossils afford proof of varied physical conditions? Give a reason for some rocks being more barren of fossils than others.
89. State some of the characters which distinguish broadly the older fossiliferous strata from those similar accumulations which are being formed in our own day.
90. How may we identify formations in separate districts? How is the interrupted and partial distribution of strata to be accounted for?
91. In what respect do the fossils in younger strata differ from those in older strata? What general proof can be adduced to shew that species have become gradually extinct?
92. Give an instance how fossils prove changes of climate in the past. What is supposed to be the cause of great cosmical changes of climate? Describe Mr Croll's theory of cosmical changes of climate.
93. What is the test of superposition? Mention another test of the relative age of strata.
94. Name the four great divisions under which the fossiliferous rocks are arranged.
95. Name the Primary or Palæozoic formations. What are the principal kinds of fossils found in the Old Red Sandstone? Which formation is the chief repository of coal in Britain?
96. In what other formations do coals occur? In which formation do the oldest known mammals occur? Name the Secondary formations.
97. Name the Tertiary formations. What kind of climate characterised the northern hemisphere at the beginning of Pleistocene times? What kinds of climate would appear from the evidence to have chiefly prevailed in Primary, Secondary, and Tertiary ages? Have we any trace of frigid conditions during these ages? What is the growing opinion with regard to the climatic conditions during the glacial period of Pleistocene times?
[A] There are various kinds of felspar; the one referred to above is orthoclase, or potash-felspar.
[B] It is needless to describe the minerals minutely here. The student can only learn to distinguish the different species by carefully examining actual specimens.
[C] Petros, a rock, and logos, a discourse. Some geologists restrict this term to the study of the structure and arrangement of rock-masses, and apply the term lithology (lithos, a stone, and logos, a discourse) to the study of the mineralogical composition of rocks.
[D] The degree of inclination is very variable. It may occur at almost any angle up to vertical. But, as a rule, the hade of the more powerful faults is steeper than that of minor displacements.
[E] Igneous rocks have also in some cases undergone considerable alteration; fine-grained tuffs, for example, occasionally assume a crystalline texture.
[F] Palaios, ancient, onta, beings, and logos, a discourse.
[G] To this there are some exceptions. Certain small foraminifers, for example, met with in some of the oldest formations, do not seem to differ from species which are still living. The genus Lingula (Mollusca) has also come down from remotest ages, having outlived all its earlier associates.
[H] This holds strictly true, however, only in regard to comparatively limited areas. The student must remember that strata occurring in widely separate regions of the earth, even although they contain very much the same assemblage of fossils, are not necessarily contemporaneous, in the strict meaning of the word; for the fauna and flora (the animal and plant life) may have died out, and become replaced by new forms more rapidly in one place than another. The term 'contemporaneous,' therefore, is a very lax one, and may sometimes group together deposits which, for aught that we can tell, may really have been accumulated at widely separated times.
[I] Apo, away from; hēlios, the sun.
[J] Peri, round about or near by; hēlios, the sun.