POST-TERTIARY FOSSILIFEROUS DEPOSITS. 23 



Peden Islandicus being often covered with large Balani, which must have been broken 

 had they been drifted. 



In exposed situations there must have been contemporaneous beds of gravel in which 

 the Moll usca* were rolled and broken and Ostracoda could not live. An example may be 

 seen in the railway-cutting near Drymen, Stirlingshire (140 feet above the sea), where a 

 gravel bed has been exposed, full of hinges and fragments of the shell of Ctjprina Islandica, 

 fragments of Peden Islandicus, Astarte sulcata, Biiccinum undatum, and other bivalves, 

 while only a few univalves, like Tropkon clathratus, are entire, and Entomostraca are very 

 scarce. 



Very frequently these Arctic Post-tertiary clays, especially in the west of Scotland, 

 rest upon an unfossiliferous Boulder Clay, a thin seam of laminated clay alone interposing, 

 and are overlain by beds of sand and gravel, followed by peat and surface soil. 



The Boulder Clay throughout the whole district is violently undulated ; and the over- 

 lying beds of the Arctic shell clay commonly rest in the hollows of the Boulder Clay, 

 although in some instances, as at Jordan Hill and Airdrie, they attain the heights of 

 63 feet and 526 feet respectively. 



The laminated clay which so frequently interposes between the Boulder Clay and the 

 clay in which an Arctic marine fauna most abundantly occurs may be clearly seen in this 

 position at Paisley, along the shores of Gareloch and Loch Long, at Kilchattan, and 

 throughout the Kyles of Bute. The Boulder Clay beneath it, in all these localities, is 

 uniformly azoic, while the clay immediately above it is literally packed with Arctic 

 Moll usca and swarms with Ostracoda. 



This laminated clay was formerly supposed to be unfossiliferous ; we have, however, 

 detected in it several species of Foraminifcra and Ostracoda. When the specimens are 

 extremely rare, it generally happens that they consist of Foraminifera only, but when they 

 prevail to any slight extent Ostracoda are also found. 



This laminated clay was probably deposited by the cold and rapid waters of streams 

 issuing from beneath the snow and ice of an elevated land surface, and carrying to the 

 sea the fine mud with which they were charged. 



The way in which it has happened that the laminated clay itself contains so few 

 fossils, while the clay immediately above it abounds with Ostracoda and MoUusca, is 

 explained by observations made in the Arctic regions by Dr. Robert Brown, of 

 Campster.^ 



Dr. Brown has had large opportunities of examining ice-action, and draws the 

 distinction between the " ordinary stratified azoic clay and the finer stratified fossiliferous 

 clay," upon which we have been led by our study of the Scotch beds to insist ; while he 



^ " On the Physics of Arctic Ice, as explanatory of the Glacial Remains in Scotland." By Robert 

 Brown, of Campster, M.A., Ph.D., F.R.G.S., &c. ' Quarterly Journal of Geological Society,' 1871, 

 \ol. xxvi, p. 671. 



