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.