154 Mr. Smith on the Relative Age of the Tertiary and 



species. The same order of superposition is observable in the basins of the Forth 

 and the Tay, and although scarcely anything has been done in the investigation 

 of the marine remains imbedded in their elevated deposits, I have little doubt that, 

 from their exact agreement, both in position and in mineral structure, they will be 

 found to be of the same age as those of the Clyde*. Should they prove to be 

 identical, the submarine forest of the Tay must also belong to the tertiary period, 

 being overlaid by the stratified marine beds. 



These deposits pass from below the present level of the sea to an elevation 

 which has not been ascertained. In Scotland organic remains belonging to them 

 have been found at the height of 350 feet ; and if the elevated terraces of Glenroy 

 are of marine origin, they probably belong to the same period, and indicate a 

 change of upwards of 1000 feet. I am convinced that a very great proportion of 

 the superficial beds of sand, gravel and clay, as well as the unstratified till or di- 

 luvium, are tertiary ; although where organic remains are wanting, there must 

 always be some uncertainty. During the succeeding or post-tertiary period, a 

 movement of elevation of about 40 feet must have taken place. At this height 

 (40 feet) the sea appears to have been stationary for a length of time greatly 

 exceeding the present period of repose. This is indicated by a magnificent range 

 of inland sea cliffs, with beds of gravel and sand interposed between them and 

 the sea. All the testacea hitherto discovered in these beds agree with existing 

 species in the British seas ; the number of shells collected from them amounts 

 to about 160. I was at first led to suppose that they contained a small propor- 

 tion of unknown species, latterly there was only one to which I could not assign 

 a living analogue, viz. Area papillosa, but on that point there is now no doubt ; 

 for, within these few weeks, Captain Portlock sent me a specimen which he had dis- 

 covered recent on the coast of Ireland. The raised beaches of the period imme- 

 diately preceding the last changes of level in the basin of the Clyde, do not there- 

 fore contain any mixture of unknown shells, although probably accumulated long 

 anterior to the recent period. 



During the existing geological epoch, no change of level appears to have taken 

 place in this locality, whilst there is direct evidence that, at least as far back 

 as the time of the Romans, it was precisely the same as at presentf. 



I subjoin a list of the marine shells which have been found in these beds, and 

 which are not known as inhabitants of the British seas. In stating the proportion 

 which they bear to the recent British species, I have made allowance for the pro- 

 bability of some of them being still inhabitants of our seas, although, as yet, 



* This is partly confirmed by the Nucula pygmcea, one of the unknown shells of the Clyde beds, 

 having been found in the elevated beds of the Tay by Mr. Lyell. 

 t See Proceedings, vol. ii. p. 427. 



