Correspondence. 37 



The immense territory in North America — several hundred thou- 

 sand square miles in extent, underlain by the formations mentioned 

 above, in an imaltered state — assures the world that the petroleum 

 of the New World, like the coal, is probably practically inexhaustible. 



6. Petroleum is unquestionably of organic origin. In my opinion 

 the great mass of it has been derived from plants ; but some think 

 it comes from animals, being either a fish-oil or a substance related 

 to adiposcere. It does not appear to be the result of a natural dis- 

 tillation of coal, since its chemical composition is different from the 

 oil manufactured artificially from the cannels, containing neither 

 nitro-benzole nor aniline. Moreover, petroleum occupied fissures in 

 the Silurian and Devonian strata long before the trees of the Coal 

 period were growing in their native forests. The nearly universal 

 association of brine with petroleum, and the fact of the slight 

 solubility of hydro-carbons in fresh, but insolubility in salt water, 

 excite the inquiry whether the salt-water of primaeval lagoons 

 may not have prevented the escape of the vegetable gases beneath, 

 and condensed them into liquids ? The hint appears to be worthy 

 of consideration. 



cos-ieiESiPOisriDEisrciE]. 



To the Editor of the G-eological Magazine. 

 Sib, — The faults in the Dkipt at Hitchin, made the subject of 

 correspondence in your Magazine, were shewn by me in the litho- 

 graphic sections accompanying the map of the Drift of the East of 

 England, which I printed for private distribution in May, 1865 ; and 

 a copy of which is in the libraries of the Geological Society, of the 

 Woodwardian Professorship, and of those of most other scientific 

 bodies. This was more than a year before Mr. Salter, unacquainted, 

 as I understand, with that work, had his attention attracted by them. 

 I now write to call your readers' attention to the fact that the most 

 striking features of the Hitchin section do not appear in Mr. Salter's 

 paper. The sand and gravel which has been slightly faulted at the 

 Station, is that which, in thickness varying from twenty-five to sixty 

 feet, underlies the wide-spread Boulder-clay (termed by me the Upper 

 Drift) over most of the East of England ; but which has a mpre 

 limited extent in the north-east portion of the Central Counties, 

 where the upper Drift rests most frequently on the older rocks. 

 Now this sand and gravel (or middle Drift) is always strictly con- 

 formable to the upper Drift ; and over western Hertfordshire lies 

 generally at the surface, owing to the denudation of the upper, which 

 there occurs only in outliers. In the centre of Herts, between Bal- 

 dock and Buntingford, and for some way south of the latter place, it 

 is generally absent, the upper Drift resting on the Chalk. If any of 

 your readers will walk up the Great Northern Eailway, from Hitchin 

 to Hatfield, they will see, at Wymondley cutting, this middle Drift 

 rising up sharply from beneath the upper, and (except where it is 

 capped, near Stevenage, by the upper) occupying the cuttings as far 



