ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixxxi 



in the interior of the mineral masses themselves. An illustrative 

 example of this fact is to be found in the chalk beneath the Lon- 

 don clay, on which, with its covering of gravel, we are now assem- 

 bled. The springs from the chalk, where it crops out to the north, 

 west, and south of us, show no want of the bicarbonate of lime in 

 solution ; it is sufficiently abundant ; but in the water of the wells 

 which have been sunk in London through the clay into the chalk 

 this substance is scarce, and has even been found absent. In the 

 well. at Trafalgar Square out of 68*24 grains of solid matter in an 

 imperial gallon, 3' 255 only were carbonate of lime, while there were 

 1 8 grains of carbonate of soda ; and, as illustrating the dissemination 

 of chloride of sodium, 20 grains of that substance. In the deep well 

 at Camden Town, also in the chalk, out of 44 grains of solid matter 

 in an imperial gallon, 17' 6 were composed of carbonate of soda, ITl 

 of chloride of sodium, and no trace of carbonate of lime was de- 

 tected*. 



To explain these interesting circumstances Dr. Lyon Playfair has 

 suggested to me that the first effect arising from water containmg 

 carbonic acid, and filtering through chalk in which there was silicate 

 of potash or soda, would be to dissolve the carbonate of lime, so that 

 if soon thrown out as s])ring-water it would contain the bicarbonate 

 of lime in solution. AVhen however this water percolated through 

 a very extended bed of chalk (containing an alkaline silicate as the 

 chalk usually does), the free carbonic acid in the water would seize 

 the alkali and form a carbonate, while the carbonate of lime deprived 

 of its solvent would fall down. Hence it is, he concludes, that the 

 deep well water of London obtained from the chalk beneath the Lon- 

 don clay is comparatively soft, containing only a few grains of bicar- 

 bonate of lime, and even sometimes none at all, while carbonate of 

 soda is found in considerable abundance, as also some free silica. 

 Alluding to the observations of Mr. Clutterbuck, who found that 

 there was an intimate connexion between the fall of water at AVatford 

 and the deep wells in London, the wells at Watford rising on Monday 



action, or to any circumstances decomposing the salt, the less amount of chloride 

 of sodium, all other conditions being the same, should we expect to find in the 

 springs from such rocks. Among those other conditions we should have to regard 

 as important the relative porosity of rocks and their exposure to atmospheric 

 waters, ^vhich should abundantly percolate through them, and not readily run off 

 their exposed surfaces. 



* The following are the analyses of the waters at the wells in Trafalgar Square 

 and Camden Town, the first by ^Messrs. Abel and Rowney, the second by Mr. 

 Richard Phillips : — 



Trafalgar Square. Camden Town. 



Carbonate of lime 3*255 



Phosphate of lime 0-034 



Carbonate of magnesia 2-254 



Sulphate of potash 13*671 



Sulphate of soda 8*749 13*00 



Chloride of sodium 20*058 IMO 



Phosphate of soda 0*291 



Carbonate of soda 18*049 17*60 



SOica 0-971 trace. 



Organic matter 0*908 2*30 



VOL. V. PART I. f 



