OF THE LEVEL OF THE SEA. 85 



cene." There can, I think, be no question as to the prac- 

 tical convenience of this rule, in judging of the age of a de- 

 posit. If the distinction of the tertiary beds, and those now 

 forming, depends upon the difference of organic life, and I 

 know of no other, and if we find a perceptible difference 

 amongst the testacea, we may conclude a fortiori that there 

 must be one still greater amongst the mammalia, because 

 every observation hitherto made concurs in this. But 

 whether we look to the absence of human remains or works 

 of art, the occurrence of extinct or unknown shells, or of 

 extinct land animals, we must conclude, that the organic 

 remains of the deposits I have been describing belong to a 

 different zoological era from the present — to that which Mr 

 Lyell has termed the newer pliocene. 



I shall now briefly notice, in the ascending order, the 

 different members of this deposit as they occur in the cen- 

 tral district, or great coal-field of Scotland. 



Resting immediately on the carboniferous strata, we find, 



1st, The stratified alluvium formerly mentioned as occa- 

 sionally to be met with under the till. It consists of beds 

 of sand, gravel, and clay, and is apparently of marine ori- 

 gin. No organic remains have yet been found in them, 

 but they seldom occur in beds of pure sand or gravel such 

 as these, and there are only a few insulated patches, the 

 remains evidently of the alluvial covering, which has been 

 removed by the same cause which lodged the till or dilu- 

 vium on the surface. 



2d, The diluvium or till.* 



* For accounts of the diluvial deposits in Scotland, see Mr Bald s 

 description of it, under the name of the old alluvial cover, in his obser- 

 vations on the coal-formation of Clackmannanshire, Wern. Mem. vol. i. 

 p. 48.1, and vol. iii. p. 105, and in his notice of the fossil elephant, ib. 

 vol. iv. p. 58. See also Colonel Imrie's paper on the geology of the 

 Campsie Hills, in which there is an excellent desci'iption of the grooves 



