4 



POST-TERTIARY ENTOMOSTRACA. 



of the beds we have exammed. Shell-beds have also been found, under circumstances 

 needing special local examination, intercalated between masses of Boulder Clay of the 

 same character. 



The only cases in which a Boulder Clay physically analogous to that of which we are 

 treating contains fossils are those which will presently be described as a second type of 

 Boulder Clay, which forms cliffs near the shore and never extends beyond a few miles inland. 



Whatever explanation of its origia may be given, so far as present investigations 

 extend, there seems to be ample evidence for the existence of a Boulder Clay : (I) Older 

 than the stratified clay containing Arctic shells ; (2) extending to far greater heights than 

 either any fossiliferous Boulder Clay or any stratified clay ; (3) unsubjected to any action 

 of the tidal wave upon the shore ; (4) and connected with the more remote and extreme 

 Arctic conditions of the Glacial Epoch. 



T/ie position of the beds from which we have obtained Ostracoda in relation to this 

 Boulder Clay will at any rate furnish a guide available for the practical use of the 

 advocates of any theory regarding their succession, which may be in debate. 



II. There oxii fossiliferous Boulder Clays which have several striking peculiarities. 



1. They occur (so far as we yet know) either close to the coast or within a distance of 

 four or five miles, and generally form low cliffs immediately on the shore. They may be 

 seen on the north-east coast of Scotland, along the north-east coast of Ireland, on the 

 north-east coast of England, on the Lancashire coast, and along the banks of the Mersey. 



2. The shells they contain are very seldom perfect, except in the case of a univalve, 

 like Turritella communis ; and, even when perfect, they are not found in their natural 

 living position. These features form a remarkable contrast to the state of the fossils in 

 the great shelly beds resting upon the Boulder Clay in the Clyde districts. In those 

 beds mimerous specimens of such Molluscs as Saxicava {Pano^aa) Norveyica, and 

 Mya TJddevallensis are foimd in their natural upright position, with fragments of the 

 syphon preserved ; while Fecten Isla7idicus, Astarte sulcata, and almost every other 

 bivalve, together with the Ostracoda, occur with united valves ; and in many cases, when 

 they are taken freshly from the clay, the connecting ligament may be detected, although 

 it quickly decays on exposure to the air. 



3. The fauna is sometimes less Arctic in character than that yielded by the stratified 

 glacial clay immediately resting upon the lowest unstratified Boulder Clay. The 

 Caithness Boulder Clay, which reaches a thickness of more than 100 feet, contains 

 (writes Mr. Jamieson) "remains of sea shells all through it, often from top to bottom, 

 and these shells are broken, rubbed, and scratched, evidently by the same agency that 

 marked the rocks and boulders," while " the group is the most modern, except that of 



