380 Mr Smith on the Changes of the Level of the Sea. 



his parish ; and Mr Witham sent me a collection from similar 

 beds on the Yorkshire coasts. In order to render the compa- 

 rison between the existing and more ancient races of testacea as 

 exact as possible, I determined, at the suggestion of Mr Lyell, 

 to avail myself of the facilities which the possession of a yacht 

 afforded, to collect and form a catalogue of those now existing 

 in the same seas. Amongst the shells dredged up, several new 

 species have been discovered. I failed, however, in finding any 

 of the unknown subfossil ones. As by far the greatest number 

 of the shells, from the ancient deposits, have been found in the 

 basin of the Clyde and north of Ireland, I have confined the 

 catalogue of recent shells to those which are now to be found in 

 the same seas ; a comparison of the two catalogues will thus 

 shew how far their former inhabitants coincide with the existing 

 species. 



In the prosecution of this inquiry, I discovered marine re- 

 mains so frequently, that any attempt to describe or enumerate 

 the localities would exceed the bounds of this paper. When 

 once I was furnished with a clue, I found them in places where 

 their presence had never before been suspected ; sometimes in 

 great numbers, whilst at others the very same beds were alto- 

 gether destitute of them. This is peculiarly remarkable in a 

 finely laminated clay, which I have traced to a great extent in 

 the counties of Lanark, Renfrew, and Dumbarton. It is equi- 

 valent to the carse clay of the Forth and Tay, and must have 

 been deposited at the bottom of a tranquil sea, at such a depth 

 as not to have been disturbed by the agitations of the surface. 

 The shells and other marine remains with which it abounds are 

 almost invariably found in the lower part of this bed, a circum- 

 stance which can only be accounted for by supposing a sud- 

 den depression, which has converte^^ a half- tide deposit into a 

 deep-sea one. The testaceous animals have thus been entomb- 

 ed alive in the beds subsequently formed, and their remains 

 are preserved with all the perfection of recent specimens. As- 

 sociated with this clay, we frequently find extensive beds of 

 pure gravel and sand also destitute of organic remains, although 

 there can be no doubt of their marine origin. Mr Lyell has ob- 

 served the same thing in similar beds in Sweden.* 



♦ Phil. Trans. 1836, pp. 11 and 15. 



