1850.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



203 



Asa triflins illustration of the intimate connection of geological 

 facts with our pursuits, we give the following: — 



"The whole quantity of water in the chalk of England north of 

 the Wealden anticlinal must be enormously great, but is hardly 

 calculable. At the very lowest conceivable estimate, considering 

 the total area as 6000 square miles, the mean thickness only 300 

 feet, and only one-third of this fully saturated to the extent of 

 one-fourth its volume, it would amount to twenty-five millions of 

 millions of gallons; while the annual supply from rain to the 

 extent of six inches of water absoibed per annum over an area of 

 2000 square miles, would amount to nearly 1 75,000,000,000, or more 

 than TToth part of the whole quantity of water contained. If the 

 popiilition of the chalk districts, including the whole area covered 

 by London clay and gravel, be taken at 4,000,000 of individuals, 

 and fifty gallons per day be allowed for each, a very large and 

 sufficient quantity for all possible sanitary purposes, there will 

 ttius be needed only about 72,000,000,000 gallons per annum for 

 this purpose, or not much more than a third of the estimated 

 annual supply from rain, and only ^jjth part of the quantity 

 contained in the rock. It is unnecessary to state that only a part 

 of this is directly available; but there must be a very large propor- 

 tion that could be pumped out, although it may be a very different 

 question as to how far this mode of obtaining water on a large scale 

 is economical, or in other respects advisable. 



'•In the above estimate the quantities throughout are reduced to 

 the very lowest that can be imagined, to show that the supply of 

 water must be much greater than any demand that can arise. In 

 point of fact, the proportion of rain entering the rock is more likely 

 to be 12 inches than 6; the mean thickness of chalk might fairly 

 have been taken at 600 feet instead of 300; and the quantity of 

 water contained, instead of being taken at one-twelfth, may have 

 been considered one-sixth of the bulk. Estimated in this way, the 

 quantity of water in the chalk would be 100,000,000,000,000 gallons, 

 and the' annual supply 350,000,000,000. In addition to the quantity 

 of rain, a large supply of water must enter some parts of the chalk 

 from mere absorption from the atmosphere. 



"The quality of water is unquestionably affected by the rocks 

 through wliich it passes: although in this respect it is not always 

 safe to conclude what the result will be without actual investiga- 

 tion. Thus water obtained from surface-deposits is almost sure to 

 contain in solution some of those organic substances which in 

 cultivated land must always abound, and which are always carried 

 down to some little distance by the descending supply of rain; 

 water from irony rocks, whether sand or otherwise, being generally 

 chalybeate, and that from calcareous rocks holding carbonate and 

 other salts of lime in solution. But when we examine the analyses 

 of different rocks, as given in previous tables, there will be found 

 also a number of other ingredients, as salts of soda, potash, 

 magnesia, and other substances, and these will also be taken up, 

 while the very action of water and the decompositions otherwise 

 going on, produce sulphuric acid, and thus again act upon the 

 containing rock, or alter combinations already in solution in the 

 water. Thus it results, that in wells, however the water is 

 obtained, there will be a certain proportion of saline and other 

 ingredients, although the actual quantity may be less in amount 

 and different in character in the case of deep and shallow wells in 

 the same locality. 



"It appears from a paper by Professor Brande, in the 'Quarterly 

 Journal of the Chemical Society,' vol. ii. p. 345, that a well was 

 sunk 42G feet deep, into 202 feet of chalk to supply the Mint. This 

 well was completed 1st of January, 1S47. The water rises to 

 within 80 feet of the surface, and about 15,000 gallons per day are 

 obtained; the level being then reduced by this amount of exhaustion 

 to about 100 feet from the surface. 



"Before the water was obtained from the chalk it yielded It 

 gi'ains of dry saline matter in the gallon of water. Since the well 

 was finished the quantity is only 37-t! grains: — SG at 55^=1000-70." 



On Mining there is very copious instruction, and fi-oni this part 

 we take another illustration. 



"Another fact to be considei'ed by the practical miner, is that 

 of the singularly frequent disturbances that have affected the beds 

 of coal and the strata associated with them, and the remarkable 

 complication of the faults that characterise many coal-fields. It 

 must not be supposed that the effect of these disturbances is either 

 uniformly advantageous or always disadvantageousto the immediate 

 interests of the miner; but there cannot be the slightest doubt that 

 we are indebted to such disturbances for frequent repetitions of the 

 same bed of coal at the surface, when without tliem it would be so 

 far covered up by newer deposits as to be utterly unattainable. 



If occasionally the miner, in prosecuting his labours, or the mine- 

 owner in following what he considers a valuable seam of coal, is 

 suddenly stopped by coming in contact with a fault, and finds the 

 coal shifted several yards above or below, or even completely lost, 

 he must not forget that it is perhaps owing to these very shifts that 

 the outcrop has taken place at all in his neighbourhood, and that 

 the coal is workable in the district in which he is interested. 



"But there is another important advantage derived from the 

 existence of these numerous faults in coal strata, namely, that they 

 intersect large fields of coal in all directions, and by the clayey 

 contents which fill up the cracks accompanying faults, become 

 cofferdams, which prevent the body of water accumulated in one 

 field from flowing into any opening which might be made in it from 

 another. This separation of the coal-field into small areas, is also 

 important in case of fire, for in this way the combustion is pre- 

 vented from spreading widely, and destroying, as it would otherwise 

 do, the whole of the seam ignited. 



"An instance of the advantage resulting from the presence of a 

 great line of fault, occurred in the year 1825, at Gosforth, near 

 Newcastle, where a shaft was dug on the wet side of the great 

 ninety-fathom dyke, which there intercepts the coal-field. The 

 workings were immediately inundated with water, and it was found 

 necessary to abandon them. Another shaft, however, was sunk on 

 the other side of the dyke only a few yards from the former, and in 

 this they descended nearly two hundred fathoms without any 

 impediment from the water." 



A Catechism of the Steam-Engiae. By John Boukne, C.E. Third 



Edition. London: Longman, 1850. 



We are glad to see the third edition of this work. AV^e noticed 

 it favourably on its first appearance, and it has since received 

 several improvements. 



Practical Ventilation, as applied to Public, Domestic, and igriculturul 

 Structures. By Robert Scott Burn, Engineer. London and 

 Edinburgh: Blackwood, 1850. 



We had intended to notice this woi-k at some leng-th, for the 

 subject is of practical importance, but unfortunately we are com- 

 pelled to postpone this design until next month. In the meantime 

 we may observe, that though the author has not announced any 

 new doctrine, he appears to have collected very judiciously the 

 opinions of Rumford, Tredgold, Arnott, Reid, and others, and 

 to have put them in a shape suitable for tlie practical man. 



FKOCSSIOINaS OF S\iZS:.Ni:iTlG socistzss. 



INSTITUTION OF CIVIL ENGINEERS. 



April 30. — William Cubitt, Esq , President, in the Chair. 



Ti'.e paper read was " On the Absorbent Power of Chalk, and its Water 

 Contents, under different Geological conditions." By Professor U. T. 



ANsTED, 



After esplaiuing the nature and extent of the chalk rock of England, 

 hoUi geologically and topographically, and briefly desoiiijing its cliicf 

 physical peculiarities, the author proceeded to detail the results of sonie 

 experiments made for the purpose of ascertaining the positive and relative 

 absorbent powers of different kinds of chalk, when exposed to moisture 

 under various circumstances. 



The specimens experimented on were small cubes, each weighing from 

 three to four ounces, taken from different dibtricts and geological posi- 

 tions, in the upper, niidJIe, and lower beds of the chalk. 



From these experiments, it appeared, that the upper chalk, when it was 

 to all appearance perfectly dry, contained about one-third part of a pint 

 of water in each rube foot, which was never parted with under any con 

 ditions of dryness of the atmosphere ; that in tlie case of an exposed sur- 

 face of the rock, the absorption from a moist atmosphere would be unim- 

 portant, although when water was presealed to it in a liquid form, the 

 upper chalk was found capable of receiving into its mass a quantity of 

 water amounting to more than two gallons for every cube foot of rock, 

 beyond the quantity usually contained iu apparently dry chalk, under 

 ordinary exposure. 



A specimen of the middle chalk, when thoroughly airdried by six 

 months' exposure, was found to contain about 23 parts water in 1000 parts ; 

 three-fourths of which water were readily given off by subsequent expo- 

 sure to a perfectly <\ry atmosphere, very little more than the original 

 quantity being re-absorbed ou exposure to a saturated atmosphere ; show- 



28* 



