80 POST-TERTIARY ENTOMOSTRACA. 



The range of Mytilus edulis is given by Mr. J. Gwyn Jeffreys as " From high-water 

 mark to the depth of a few fathoms."^ The bed occurs in the lower part of some of 

 the Arctic deposits, and in the upper part of others. 



The Mytilus edulis bed was found resting on the surface of a glacial clay, itself 

 covered by forty-two feet of Boulder Clay, on Oakshaw Hill, Paisley, sixty-four feet 

 above the mean sea-level. Dr. Eraser states that he has found a similar bed " under 

 the late steeple at the Cross of Paisley, at a height of forty feet above the sea-level ; 

 another at the head of St. Mirren Street at thirty-two feet ; another in James's Street 

 at twenty-three feet ; and another in Causey-side at a height of only twelve feet ; while 

 out in the plain, and nearer the Clyde, he had found a fringe of shells, seaweed, &c., 

 which marked the tidal limit, subsequent, of course, to the time when the lowest of these 

 beds was formed." ^ 



C. — Among the Post-tertiary fossiliferous beds of Scotland there is not only this vast 

 series of Arctic sands and clays (in themselves possibly marking various points in the 

 passage of a great epoch), but there is also a series of beds, of later date and not 

 IN ANY WAY Arctic in character, which indicate the steps through which the 

 present climate and physical geography of Scotland have been reached since 

 the final retreat of the ice. 



During the complex conditions arising from the subsidence and emergence of the 

 land, it does not seem reasonable to suppose that the climate of Scotland was ameliorated 

 by unbroken stages. A season of less heat may have been followed by a season of 

 greater heat than even now exists, in its turn to be modified by the changed dis- 

 tribution alike of the currents of the waters and the respective areas of the land 

 and sea. 



I. 8ome deposits, belonging to the class now under consideration, mag, indeed, be quoted 

 as furnishing indications of a climate certainly far frmn Arctic, and possibly of a more 

 genial character than noio prevails in Scotland. 



1. Blair Drummond, Valley of the Forth. 



The following section is given on the authority of Mr. Jamieson :* 



1. Sandstone rock. 



2. Glacial beds. 



1 'British Conchology,' vol. ii, p. 105. 



2 'Trans. Geol. Soc. Glasgow,' vol. iv, p. 180. 



3 ' Quart. Journal Geol. Soc.,' vol. sxi, p. 185, 1865. 



