OF THE LEVEL OF THE SEA. 51 



servations, led me to imagine that the term " recent," which 

 had usually been applied to such deposits, was perhaps not 

 rigidly correct. In order to ascertain how far it was so, I 

 determined to collect as many of the shells belonging to 

 them as I could. In a fresh excavation I made at Dalmuir, 

 I increased the number of species, from that locality alone, 

 to upwards of seventy. The Rev. Mr Landsborough of 

 Stevenston, in Ayrshire, was kind enough, at my request, 

 to collect marine remains from the elevated shelly deposits 

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

 similar beds on the Yorkshire coasts. In order to render 

 the comparison between the existing and more ancient races 

 of testacea as exact as possible, I determined, at the sug- 

 gestion 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 disco- 

 vered. 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 cata- 

 logue 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 

 remains so frequently, that any attempt to describe or enu- 

 merate 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 altogether destitute of them. This is peculiarly 

 remarkable in a finely laminated clay, which I have traced 



