250 ORGANIC REMAINS IN SCOTCH BOULDER CLAY. CHAP. Xitl. 



Fis. 35 



We also seem to have a test of the comparatively modern 

 origin of the mounds of till which surround the above-men- 

 tioned chain of lakes (of which that of Forfar is one), in 

 the species of organic remains contained in the shell-marl 

 deposited at their bottom. All the mammalia as well as 

 shells ai*e of recent species. Unfortunately, we have no in- 

 formation as to the fauna which inhabited the country at the 

 time when the till itself was formed. There seem to be only 

 three or four instances as yet known in all Scotland of mam- 

 malia having been discovered in boulder clay. 



Mr. E. Bald has recorded the circumstances under which 

 a single elephant's tusk was found in the unstratified drift of 

 the valley of the Forth, with the minuteness which such a 

 discovery from its rarity well deserved. He distinguishes 

 the boulder clay, under the name of the "old alluvial cover," 

 from that more modern alluvium, in which the whales of 

 Airthrie, described at p. 53, were found. This cover he 

 says is sometimes one hundred and sixty feet thick. Having 

 never observed any organic remains in it, he watched with 

 curiosity and care the digging of the Union Canal between 

 Edinburgh and Falkirk, which passed for no less than twenty- 

 eight miles almost continuously through it. Mr. Baird, the 

 engineer who superintended the works, assisted in the inquiry, 

 and at one place onl}' in this long section did they meet with 

 a fossil, namely, at Cliftonhall, in the valley of the Almond. 

 It lay at a dejith of between fifteen and twenty feet from the 

 surface, in very stiff clay, and consisted of an elephant's 

 tusk, thirty-nine inches long and thirteen in circumference, in 

 so fresh a state that an ivory-turner purchased it and turned 

 part of it into chessmen before it was rescued from destruction. 



