TEAN"SACTIO:^S 



OF THE 



WATFOED NATUEAL HISTOEY SOCIETY. 



VOL. I. 



1. — The Ceetaceous Eocks of Engianb. 

 By J. Logan Lobley, F.G.S., F.R.G.S. 



[A Lecture delivered lltli March, 1875.] 



Geology is one of the sciences for the promotion of the study of 

 which this Society has been founded ; and the investigation of the 

 geological features of Hertfordshire will doubtless engage a large 

 share of your attention. As a preparation for the due observation 

 of the geological phenomena of the district, I have been requested 

 to bring before your notice the outlines of what is known respect- 

 ing that most interesting group of rocks of which the Chalk, so 

 familiar to the iohabitants of this neighbourhood, is the principal 

 member. 



Not more than half a century since, the rocks of the earth were 

 thought to be without order or arrangement; but about this 

 time, William Smith, the uncle of a most worthy successor, who 

 died only last year. Professor Phillips, published to the world the 

 great discovery that a certain order of superposition prevailed, and 

 that strata might be identified by the organic remains which they 

 contained. From that time to the present geologists have 

 assiduously explored the rocks in this and other countries, and 

 have carefully studied the fossils which their researches have 

 brought to light. These investigations have revealed the order 

 and method of the formation of the rocks composing the crust of 

 the globe. The most important results of the researches of 

 geologists in our own country are shown by the diagrams and 

 maps now exhibited. Though the geological scale or table of the 

 sedimentary rocks represents a very definite order of arrangement, 

 it must not be supposed that all the steps of the ladder, so to 

 speak, are to be found in all places. Denudation, or the action of 

 the atmosphere, rain, rivers, and ice, through long periods of time, 

 has so worn and removed the uppermost portions of the rocks, and 

 so many movements consequent upon subterranean forces have 

 occurred, that any one of the rocks named in the scale may be 

 found at the surface. Nay more, so many and so great changes 



VOL. I. FT. I. I 



