318 The Scottish Naturalist. 



out. In Britain, also, distinct heights at which ancient Arctic 

 beaches occur are well made out, the lowest of which is the 25- 

 feet beach that runs somewhat regularly around both Britain 

 and Ireland. 



It should be clearly understood that there were milder periods 

 during this glacial era. Sometimes, as in Lanarkshire, well- 

 stratified deposits occur in which are found the remains of both 

 plants and animals, and yet these are superimposed upon and 

 overlain by glacial drift. Sometimes lake deposits are found in 

 similar positions containing like remains. We have been taken 

 thus far back in geologic history for an unexplained reason, 

 except that that is apparent in believing that our valley was 

 subjected to the grinding and grooving and deepening processes 

 of the glaciers, and that it indeed suffered many changes before 

 its present features were moulded ! The reason, however, of 

 this review of the glacial phenomena is that the evidences of 

 land-ice are apparent everywhere in the valley above the level 

 of the higher haugh. From the margin of this haugh on both 

 sides of the valley a thick stratum of boulder clay commences 

 and continues almost unbroken up the steeps for hundreds of 

 feet. This is filled with ice-dressed and some scratched and 

 polished pieces of stone, consisting of Gneiss and Schistose 

 rocks, traps of many kinds, and sandstones, that seem to have 

 come from a north-western direction. Some of these stones 

 are boulders of vast size, weighing many hundreds of pounds. I 

 have not found any such fragment upon the higher or the lower 

 haugh, neither anything like a pebble, excepting in the pebble 

 zones in the haugh beds. At the close of this remarkable series 

 of events, when our northern landscapes emerged from the 

 ordeal with their characteristic features newly moulded into 

 what we now see them, the historic alluvial deposits began to 

 be arranged out of the heterogenous materials that coated the 

 mountain sides and lay thickly spread upon the floor of the 

 valleys. Our Earn then began to be a river — at first a very 

 fickle stream indeed, decreasing in size in the winter and 

 swelling into a very sea in the summer by the melting of the 

 remaining alpine ice. Then the boulder clays and drifts under- 

 went a good deal of disturbance and re-arrangement, making 

 confusion in many instances worse confounded, mixing up de- 

 posits of different dates into one untranslatable mass. But the 

 Earn became at last a river subject only to the rising and falling, 

 that results from the rains and the droughts of the seasons, and 



