20 POST-TERTIARY ENTOMOSTRACA. 



shell bed of the same age, to say the least, as the later Clyde shell beds, and have 

 deposited Boulder Clay upon it. 



Whether this actually happened or not in the special cases quoted from Caithness 

 does not affect the possibility in question. 



It is equally possible that during the final recession of the ice, at points where the 

 glacier reached the sea, Boulder Clay may have been thrown over shell beds belonging to 

 the most recent period of the Glacial Epoch. 



Regarding these intercalated beds, it has also to be determined whether they occupy 

 tlieir peculiar position naturally or accidentally. 



The Boulder Clay (as has already been described) exists in great undulating ridges, as 

 well as against hillsides and in the interstices of broken ground, and often rises up in 

 hillocks and eminences, and has marine shell clay deposited in its hollows. 



It is clearly within the range of possibility that it should in some instances have been 

 undermined by the action of water or some other physical agency, and have fallen over 

 a shell bed of far later date than itself. 



In the series of sands, gravels, and clays claimed by Mr. J. Geikie as " interglacial," 

 and regarded by him, in his striking argument, as proving that many changes of climate 

 may have taken place during the accumulation of the Till and its associated deposits, few 

 of a fossiliferous character can as yet be quoted, so that a general discussion of them does 

 not fall within the limits of this paper. 



We shall notice only those examined for Ostracoda. 



1. Croftiiead, NEAR Glasgow. 



In the cutting of the Crofthead and Kilmarnock railway, beds of freshwater clay were 

 exposed which have been the subject of considerable discussion. They were described by 

 Mr. J. Geikie as interglacial, in the ' Geological Magazine' (vol. v, p. 393, vi 73, vii 53), 

 and as resting upon and covered by the " Till " (Boulder Clay). Mr. Craig in the same 

 magazine questioned whether the upper bed overlying the stratified bed was " a deposit 

 from land ice," and regarded the position of a large mass of Boulder Clay which covered 

 a part of the stratified clay as owing to " a series of slips. 



These stratified lacustrine clays yielded the skull and horn core of Bos primigenius, 

 part of the horn of Megaceros Hiberniciis, and a few bones of JEquus cahallus. 



^ See also paper on "The Section of the Crofthead and Kilmarnock Railway." By Robert Craig. 

 'Trans. Geol. Soc,,' Glasgow, vol. iv, p. 17. 



