66 Geological Society. 



trust that Mr. Francis may receive sufficient encouragement to in- 

 duce him to persevere in a labour which can, at best, be but scantily 

 remunerated. At present, we regret to legjn, he has not clear- 

 ed the expenses of publication. We would urge those of our 

 readers, therefore, who are interested in the promotion of this de- 

 partment of botanical science (as all who call themselves botanists 

 ought to be), to do what in them lies for the continued success of 

 this undertaking, calculated as it is in the highest degree for their 

 benefit. 



XL Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from vol. xvi. p. 148.] 



Nov. 6, A PAPER was afterwards read, " On the relative ages of 

 1839. -**■ the tertiary and post-tertiary deposits of the Basin of 

 the Clyde," by James Smith, Esq., of Jordan Hill, F.G.S. ; of which 

 an abstract will be found in No. 65 of the Society's Proceedings. 



A paper was last read, " On the foul air in the chalk and strata 

 above the chalk near London," by James Mitchell, LL.D., F.G.S. 



In the chalk, the most abundant deleterious gas is the carbonic 

 acid, but 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. In sinking wells, it has been noticed to 

 issue with force from one stratum, whilst none has been perceived to 

 be given out from the beds immediately above and below it. Dr. 

 Mitchell mentions fatal effects due to its occurrence in a well near 

 the race -course at Epsom, where it was met with at the depth of 

 200 feet ; and in Norbury Park, near Dorking, at the depth of 400 

 feet. On Bexley Heath, after sinking through 140 feet of gravel and 

 sand and 30 feet of chalk, it rushed out and extinguished the can- 

 dles of the workmen ; and in making a well in Long Lane, Bexley 

 Heath, after penetrating 124 feet of overlying deposits, and then 90 

 feet of chalk, considerable inconvenience was felt from it, but G feet 

 lower no gas was emitted. 



In chalk, sulphuretted hydrogen gas 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 gas is sometimes emitted, but more fre- 

 quently sulphuretted hydrogen gas. 



Carburetted hydrogen has seldom inflamed in wells, but in making 

 the Thames tunnel it has sometimes issued in such abundance as to 

 explode by the lights and scorch the workmen. 



Sulphuretted hydrogen gas is more abundant, and it has been ob- 

 served almost always to proceed from a coarse black sand charged 

 with oxide of iron, whether the bed be above the blue clay, within it 

 or below it. It has streamed out with great violence in the Thames 

 tunnel, but has in no instance produced fatal effects. At Ash, 3 miles 



