Watford Natural History Society. 281 



mountains. Supposing the ice was a mile thick, the pressure would 

 be half a ton on the inch, in the Himalaya at least, and the produc- 

 tion of water by friction of ice upon ice enormous. Friction is 

 dependent upon pressure, distance moved, and mass, and independent 

 of velocity of motion. All deep lakes must be referred for origin 

 to the Glacial, and not to the Preglacial period. They are the direct 

 consequences of the elevation of mountains in the Preglacial or 

 preceding period. 



Watford Natural History Society and Hertfordshire Field 

 Club. — March 11, 1875.— John Evans, Esq., F.K.S., President, in 

 the Chair. 



" On the Cretaceous Kocks of England." By J. Logan Lobley. 

 Esq., F.G.S. 1 



This lecture, an introduction to the Geology of Hertfordshire, 

 commenced with a reference to the great teachings of the work of 

 William Smith and his successors ; after which the stratigraphical 

 position of the Cretaceous system, and the vast area of the Earth's 

 surface within the limits of which Cretaceous deposits may be 

 found, were pointed out. 



The fan-like extension of the Cretaceous rocks in England, com- 

 mencing at the Dorsetshire coast, is marked out by the Chalk, which, 

 speaking broadly, indicates the geographical position of the English 

 Cretaceous rocks generally. 



Commencing with the Wealden, each of the great divisions of the 

 system were described. 



The Chalk, as the rock of Hertfordshire, was specially dwelt upon. 

 The calcareous Foraminiferal and the siliceous Polycistinal deposits on 

 the bed of the Atlantic canal were explained by the aid of diagrams. 



The recent researches of the " Challenger " expedition had revealed 

 the previously unsuspected occurrence of a red argillaceous mud at 

 the bottom of a submarine valley of great depth, and as this was 

 probably the residuum of Foraminiferal tests, the calcareous matter 

 of which had been prevented by some solvent process from reaching 

 these lowest depths, the hypothesis of the organic origin of clays, 

 recently enunciated by Prof. Huxley, had been suggested. The local 

 geology and the geological features of the Thames Yalley having been 

 described, the dependence of the plants of a district on its geology, 

 as shown by the presence of the fine beeches for which the 

 neighbourhood of Watford is famed, exemplifies the connexion 

 subsisting between the various natural sciences, the study of which 

 this Society is intended to promote. 



To Geology, however, and to the study of the Cretaceous rocks of 

 their own county, the members were specially urged to give their 

 attention, since wider views and greatly extended knowledge would 

 surely follow. 



The lecture was illustrated by diagrams, maps, and fossils, and 

 under the microscope recent, as well as fossil (Chalk) Foraminifera, 

 etc., were exhibited. 



1 The first communication to the Society. 



