287 



The Kimmeridge clay so well exposed on tlie Dorsetshire 

 coast, and traceable through Wiltshire, Buckinghamshire, 

 Lincolnshire and Yorkshire, is everywhere characterized by 

 Ostrea deltoidea. This formation is, comparatively speaking, a 

 barren deposit in our island, and good fossiliferous beds have 

 not yet been exposed. Our present knowledge of this great 

 argillaceous deposit is most imperfect, and until a good series 

 of its fossils is obtained it is impossible to correlate its beds 

 with those of the "Argiles VirguUennes" of the Boulonais. 



My observations have greatly exceeded the limits I had 

 originally prescribed to this memoir, and I have to apologize 

 for their unavoidable extension. I was anxious to place before 

 my associates the notes I had made in France on a subject most 

 interesting to all persons who study Jurassic Geology; and 

 especially to those of our members who have taken a part in 

 the discussions which, from time to time, have occupied our 

 attention in our many meets among the charming Cotteswold 

 Hills, — the miniature Jura of Grloucestershire. If these remarks 

 sbould perchance awaken in any of my colleagues a taste for the 

 study of Comparative Geology, my work will not have been in 

 vain. Having been for many years an earnest student of 

 Jurassic Palaeontology, in connection with my large work on 

 the Oolitic Echinodermata, I have become deeply impressed 

 with the importance of this kind of knowledge, not only to 

 those who, like myself, may take up special branches of inves- 

 tigation, — for to all such it is indispensable, — but to those also 

 who desire to acquire larger views of natural phenomena, and 

 who strive to emancipate their minds from the narrow ideas 

 and insular prejudices that unconsciously entwine themselves 

 around the observer who limits his investigations to particular 

 localities, and excludes from his enquiry any knowledge of 

 similar phenomenain other regions or other lands ; — to all such 

 persons Comparative Geology offers a vast field of investigation, 

 replete witb instruction, charming from associations and 

 recollections, and affording materials for a more philosophical 

 survey of nature, and a truer conception of the wonderful laws 

 by which the fabric of our globe has grown, and been developed 

 into its present condition. 



