POST-TERTIARY FOSSILIFEROUS DEPOSITS. 19 



The following Ostracoda were found : 



Cy flier e tuber culata (G. 0. Sars). 



— Dunelmensis (Norman). 

 Cytheridea papillosa, Bosquet. 



— puncfillata, Brady. 



— Sorbyana, Jones. 

 Cytheropteron Montr osiense, nov. sp. 



5. Thus the following classes of fossiliferous beds may be found beneath the Boulder 

 Clay, and without any observed Boulder Clay for their base : 



a. Marine sands and gravels more allied to the English Crag than to the glacial 

 clays. 



b. Beds of freshwater origin with the remains of Elephas primiyenius and Cervus 

 tarandus. 



c. Marine beds containing the common Arctic fauna of the Clyde glacial beds. 



d. Marine beds which have been broken up by some disturbing force, and some of 

 the shells from which have been mixed with the Boulder Clay under which they were 

 finally crushed. 



It does not necessarily follow from the mere position of any one of these beds beneath 

 a Boulder Clay that it must belong to an " interglacial " period ; many other considerations 

 are needed to determine this point. A Boulder Clay may have been deposited upon a 

 shell bed during some interglacial period, or during the later part of the glacial marine 

 period, according to the local circumstances of the case ; or it may even have been thrown 

 upon it by an accidental displacement long after its own original formation. 



II. Fossiliferous beds have been also found, situated between masses of Boulder Clay, 

 which have been referred (together with other sand and gravels) to a series of " Interglacial 

 deposits."^ 



The actual occurrence of fossiliferous beds between masses of Boulder Clay does not 

 prove that all sucli beds belong to the same period, or even that they were deposited in 

 the middle of the Glacial Epoch itself. 



It is possible (as instanced in Caithness) that drifting ice should have passed over a 



1 ' On Changes of Climate during the Glacial Epoch.' By James Geikie, F.R.S.E. Trubner and Co. 

 1872.—' The Great Ice Age.' By James Geikie, F.R.S.E. W. Isbister and Co., London. 



