CHAPTER VIII.
TABLES AND MISCELLANEOUS INFORMATION.

The following tabulated form shows the order of succession of the various stratified rocks with their usual thicknesses.

Groups. Strata. Thickness
in Feet.
    RECENT         1 Modern Deposits.      
    PLEISTOCENE         2 Drift and Gravel Beds     20 to 100
              3 Mammaliferous Crag     10 to 40
    PLIOCENE         4 Red Crag     30
CAINOZOIC, OR             5 Suffolk (Coralline) Crag     30
TERTIARY.   MIOCENE         6 Faluns (Touraine) Molasse Sandstones     6000
              7 Hempstead Series     170
        Upper     8 Bembridge Series     110
              9 Headon Series     200
    EOCENE   Middle     10 Barton Beds     300
              11 Bagshot and Bracklesham Series     1200
        Lower     12 London Clay and Bognor Beds     200 to 520
              13 Woolwich Beds & Thanet Sands     100
                       
              14 Maestricht Beds     110
              15 Upper Chalk     300
              16 Lower Chalk and Chalk Marl     400
    CRETACEOUS         17 Upper Greensand     130
              18 Gault     100
              19 Speeton Clay     130
              20 Lower Greensand     250
                       
    WEALDEN         21 Weald Clay     150
              22 Hastings Sands     600
    PURBECK         23 Purbeck Beds     150
    UPPER         24 Portland Rock and Sand     150
    OOLITE         25 Kimmeridge Clay     400
                       
              26 Upper Calcareous Grit     40
MESOZOIC, OR   MIDDLE         27 Coralline Oolite     30
SECONDARY.   OOLITE         28 Lower Calcareous Grit     40
              29 Oxford Clay     400
              30 Kellaways Rock     30
                       
              31 Cornbrash     10
              32 Forest Marble and Bradford Clay     50
    LOWER         33 Great Oolite     120
    OOLITE         34 Stonesfield Slate     9
              35 Fullers’ Earth     50 to 150
              36 Inferior Oolite     80 to 250
                       
              37 Upper Lias Shale     50 to 300
    LIAS         38 Marlstone and Shale     30 to 200
              39 Lower Lias and Bone Beds     100 to 300
                       
    TRIASSIC, or         40 Variegated Marls or Keuper     800
    NEW RED         41 Muschelkalk      
    SANDSTONE         42 Red Sandstone or Bunter     600
                       
    PERMIAN or         43 Red Sand and Marl     50
    MAGNESIAN         44 Magnesian Limestone     300
    LIMESTONE         45 Marl Slate     60
              46 Lower Red Sandstone     200
                       
              47 Coal Measures     3000 to 12,000
    CARBONIFEROUS         48 Millstone Grit     600
              49 Mountain Limestone     500 to 1400
              50 Limestone Shales     1000
                       
PALÆOZOIC, OR   DEVONIAN or         51 Upper Devonian      
PRIMARY.   OLD RED         52 Middle Devonian     3000 to 8000
    SANDSTONE         53 Lower Devonian and Tilestones      
                       
              54 Ludlow Rocks     2000
        Upper     55 Wenlock Beds     1800
              56 Woolhope Series     3050
    SILURIAN   Middle     57 Llandovery Rocks     2000
              58 Caradoc and Bala Rocks     5000
        Lower     59 Llandeilo Rocks     4000
              60 Lingula Flags     8000
    CAMBRIAN         61 Longmynd and Cambrian Rocks     20,000
                       
    METAMORPHIC           Clay Slate, Mica-Schist.      
AZOIC.               Gneiss, Quartz Rocks.      
    IGNEOUS           Granite.      
                       

The Quantity of Excavation in Wells
for each Foot in Depth.
(Hurst.)
Diameter of
Excavation.		 Quantity.
     
ft. in. cubic yards.
3 0   ·2618
3 3   ·3072
3 6   ·3563
3 9   ·4091
4 0   ·4654
4 3   ·5254
4 6   ·5890
4 9   ·6563
5 0   ·7272
5 3   ·8018
5 6   ·8799
5 9   ·9617
6 0 1·0472
6 3 1·1363
6 6 1·2290
6 9 1·3254
7 0 1·4254
7 3 1·5290
7 6 1·6362
7 9 1·7472
8 0 1·8617
8 6 2·1017
9 0 2·3562
9 6 2·6253
10 0 2·9089
10 6 3·2070
11 0 3·5198
12 0 4·1888
     
The Measure in Gallons, and the Weight in Pounds,
of Water contained in Wells, for each Foot in Depth.
Diameter. No. of Galls. Weight.
       
ft. in.    
2 0 19·61 196·1
2 6 30·56 305·6
3 0 43·97 439·7
3 6 60·00 600·0
4 0 78·19 781·9
4 6 98·87 988·7
5 0 122·23 1222·3
5 6 147·96 1479·6
6 0 175·99 1759·9
6 6 206·59 2065·9
7 0 239·05 2395·0
7 6 275·49 2754·9
8 0 313·43 3134·3
8 6 353·03 3533·0
9 0 395·42 3954·2
9 6 441·71 4417·1
10 0 489·93 4899·3
       

Brickwork.
The Number of Bricks and Quantity of Brickwork in Wells
for each Foot in Depth.
(Hurst.)
  Half-Brick Thick. One Brick Thick.
  Number of Bricks.   Number of Bricks.  
  Laid
Dry.		 Laid in
Mortar.		 Cubic Feet of
Brickwork.		 Laid
Dry.		 Laid in
Mortar.		 Cubic Feet of
Brickwork.
1·0   28  23  1·6198  70  58  4·1233 
1·3   33  27  1·8145  80  66  4·7124 
1·6   38  31  2·2089  90  74  5·3015 
1·9   43  35  2·7979  112  92  6·4795 
2·3   53  44  3·0926  122  100  7·0686 
2·6   58  48  3·3870  132  108  7·6577 
3·0   68  57  3·9760  154  126  8·8357 
3·6   79  65  4·5651  174  142  10·0139 
4·0   89  73  5·1541  194  159  11·1919 
4·6   100  82  5·7432  214  176  12·3701 
5·0   110  90  6·3322  234  192  13·5481 
5·6   120  98  6·9213  254  209  14·7263 
6·0   130  107  7·5103  276  226  15·9043 
6·6   140  115  8·0994  296  242  17·0825 
7·0   150  123  8·6884  316  260  18·2605 
7·6   160  131  9·2775  336  276  19·4387 
8·0   170  140  9·8665  358  292  20·6167 
8·6   180  148  10·4556  378  308  21·7949 
9·0   191  156  11·0446  398  326  22·9729 
10·0   212  174  12·2227  438  360  25·3291 
             

Good bricks are characterized as being regular in shape, with plane parallel surfaces, and sharp right-angles; clear ringing sound when struck, a compact uniform structure when broken, and freedom from air-bubbles and cracks. They should not absorb more than one-fifteenth of their weight in water.

After making liberal allowance for waste, 9 bricks will build a square foot 9 inches thick, or 900, 100 square feet, or say 2880 to the rood of 9-inch work, which gives the simple rule of 80 bricks = a square yard of 9-inch work.

The resistance to crushing is from 1200 to 4500 lb. a square inch; the resistance to fracture, from 600 to 2500 lb. a square inch; tensile strength, 275 lb. a square inch; weight, in mortar, 175 lb. a cubic foot; in cement, 125 lb. a cubic foot.

Compressed bricks are much heavier, and consequently proportionately stronger, than those of ordinary make.

Storing Well-water.

The reservoirs for storing well-water should be covered with brick arches, as the water is generally found to become rapidly impure on being exposed to the sunlight, principally owing to the rapid growth of vegetation. Various methods have been tried, such as keeping up a constant current of fresh water through them, and a liberal use of caustic lime; but so rapid is the growth of the vegetation, as well as the change in the colour of the water, that a few hours of bright sunlight may suffice to spoil several million gallons. These bad results are completely prevented by covering the reservoirs.

Hints on Superintending Well-work.

The engineer who has to superintend the construction of a well should be ever on the watch to see whether, in the course of the work, the strata become so modified as to overthrow conclusions previously arrived at, and on account of which the well has been undertaken.

A journal of everything connected with the work should be carefully made, and if this one point alone is attended to it will be found of great service both for present and future reference.

Before commencing a well a wooden box should be provided, divided by a number of partitions into small boxes; these serve to keep specimens of the strata, which should be numbered consecutively and described against corresponding numbers in the journal. At each change of character in the strata, as well as every time the boring rods are drawn to surface, the soil should be carefully examined, and at each change a small quantity placed in one of the divisions of the core box, noting the depth at which it was obtained, with other necessary particulars. A note should be made of all the different water-levels passed through, the height of the well above the river near which it is situated, as well as its height above the sea. The memoranda in the journal relating to accidents should be especially clear and distinct in their details; it is necessary to describe the effects of each tool used in the search for, or recovery of, broken tools in a bore-hole, in order to suit the case with the proper appliances, for without precaution we may seek for a tool indefinitely without being sure of touching it, and perhaps aggravate the evil instead of remedying it. It is by no means a bad plan to make rough notes of all immediate remarks or impressions, in such a manner as to form a full and detailed account of any incidents which occur either in raising or lowering the tools. At the time of an accident a well kept journal is a precious resource, and at a given moment all previous observations, trivial as they may have often seemed, will form a valuable clue to explain difficulties, without this aid perfectly inexplicable.

When an engineer has a certain latitude allowed him in the choice of the position for a well, he should not, other things being equal, neglect the advantages which will be derived from the proximity of a road for the transport of his supplies; of a well, if not a brook, from which to obtain the water necessary for the cleansing of the tools; and of a neighbouring dwelling, to facilitate his active supervision. This supervision, having often to be carried on both day and night, should be the object of particular study; well carried out, it may be effective, while at the same time allowing a great amount of liberty; badly carried out, however fatiguing it may be, it will be incomplete.

Rate of Progress of Boring.
(André.)

There are probably no engineering operations in which the rate of progress is so variable as it is in that of boring. That such must necessarily be the case will be obvious when we bear in mind that the strata composing the earth’s crust consist of very different materials; that these materials are mingled in very different proportions, and that they have in different parts been subjected to the action of very different agencies operating with very different degrees of intensity. Hence it arises not only that some kinds of rocks require a much longer time to bore through than others, but also that the length of time may vary in rocks of the same character, and that the character may change within a short horizontal distance. Thus it is utterly impossible to predicate concerning the length of time which a boring in an unknown district may occupy, and only a rough approximation can be arrived at in the case of localities whose geological constitution has been generally determined. Such an approximation may, however, be attained to, and it is useful in estimating the probable cost; and to attain the same end, for unknown localities, an average may be taken of the time required in districts of a similar geological character. The following, which are given for this purpose, are the averages of a great number of borings executed under various conditions by the ordinary methods. The progress indicated represents that made in one day of eleven hours.

            ft. in.
1. Tertiary and Cretaceous Strata, to a depth of 100 yards, average progress 1   8
2. Cretaceous Strata, without flints „ 250 „ „ 2   1
3. Cretaceous Strata, with flints „ 250 „ „ 1   4
4. New Red Sandstone „ 250 „ „ 1 10
5. New Red Sandstone „ 500 „ „ 1   5
6. Permian Strata „ 250 „ „ 2   0
7. Coal Measures „ 200 „ „ 2   3
7. Coal Measures „ 400 „ „ 1   8
    General Average   275     1   9

When the cost of materials and labour is known, that of the boring may be approximately estimated from the above averages. Should hard limestone or igneous rock be met with, the rate of progress may be less than half the above general average. Below 100 yards, not only does the rate of progress rapidly increase, but the material required diminishes in like proportion, so that for superficial borings no surface erections are needed, and the cost sinks to two or three shillings a yard.

Cost of Boring.

The cost of boring when executed by contract has already been treated of at page 80. The following formula will furnish the same results as the rule there given, but with the least possible labour of calculation;

x = 0·5d(·187 + ·0187d);

x being the sum sought, in pounds, and d the depth of the boring in yards.

Example. Let it be required to know the cost of a bore-hole 250 yards deep.

Here 125{·187 + (·0187 × 250)} = £607·75.

Tempering Boring Chisels.

1. Heat the chisel to a blood red heat, and then hammer it until nearly cold; again, heat it to a blood red and quench as quickly as possible in 3 gallons of water in which is dissolved 2 oz. of oil of vitriol, 2 oz. of soda, and 1⁄2 oz. of saltpetre, or 2 oz. of sal ammoniac, 2 oz. of spirit of nitre, 1 oz. of oil of vitriol: the chisel to remain in the liquor until it is cold.

2. To 3 gallons of water add 3 oz. of spirit of nitre, 3 oz. of spirits of hartshorn, 3 oz. of white vitriol, 3 oz. sal ammoniac, 3 oz. alum, 6 oz. of salt, with a double handful of hoof-parings, the chisel to be heated to a dark cherry red.

Gases in Wells.

The most abundant deleterious gas met with in wells is carbonic acid, which extinguishes flame and is fatal to animal life. Carbonic acid is most frequently met with in the chalk, where it has been found to exist in greater quantity in the lower than in the upper portion of the formation, and in that division to be unequally distributed. Fatal effects from it at Epsom, 200 feet down, and in Norbury Park, near Dorking, 400 feet down, have been recorded. At Bexley Heath, after sinking through 140 feet of gravel and sand and 30 feet of chalk, it rushed out and extinguished the candles of the workmen. Air mixed with one-tenth of this gas will extinguish lights; it is very poisonous, and when the atmosphere contains 8 per cent. or more there is danger of suffocation. When present it is found most abundantly in the lower parts of a well from its great specific gravity.

Sulphuretted hydrogen is also occasionally met with, and is supposed to be generated from the decomposition of water and iron pyrites.

In districts in which the chalk is covered with sand and London clay, carburetted hydrogen is occasionally emitted, but more frequently sulphuretted hydrogen. Carburetted hydrogen seldom inflames in wells, but in making the Thames Tunnel it sometimes issued in such abundance as to explode by the lights and scorch the workmen. Sulphuretted hydrogen also streamed out in the same place, but in no instance with fatal effects. At Ash, near Farnham, a well was dug in sand to the depth of 36 feet, and one of the workmen descending into it was instantly suffocated. Fatal effects have also resulted elsewhere from the accumulation of this gas in wells.

INDEX.