252 The Scottish Naturalist. 



difficulty remains. The Criffel and Cumbrian erratics suddenly 

 cease when they are followed to the south, great quantities of 

 them being accumulated over a belt of country extending from 

 beyond Wolverhampton to Bridgenorth. What was it that 

 defined the southern limits of these northern boulders? It is 

 clear that it could not have been high ground, for the Severn 

 valley, not to speak of low-lying regions further to the north- 

 east, must have been submerged according to Mr Mackintosh's 

 hypothesis. There was therefore plenty of sea-room for the 

 floating ice to escape southwards. And yet, notwithstanding 

 this, vast multitudes of bergs and floes, so soon as they arrived 

 at certain points, suddenly melted away and dropt their burdens ! 

 In what region under the sun does anything like that happen at 

 the present day? Mr Mackintosh thinks that the more or less 

 sharply-defined boundary-line reached by the erratics "could 

 only have resulted from close proximity to a persistent current 

 of water (or air?) sufficiently warm to melt the boulder-laden 

 ice." He does not tell us, however, where this warm current of 

 water or air came from, or in what direction it travelled. He 

 forgets some of his own facts connected with the appearance 

 of erratics of eastern derivation, and which, according to him, 

 point to an ocean-current that flowed across from Lincolnshire 

 into the very sea in which the Criffel granite and Cumbrian 

 boulders were being dropped. The supposed warm ocean-current, 

 then, if such it was rather than air, could hardly have come from 

 the east. Neither is it at all likely that it could have come from 

 the west, sheltered as the region of the Severn valley must have 

 been by the ice-laden mountains of Wales. Again, the south is 

 shut to us ; for there are no erratics in the south of England from 

 which to infer a submergence of that district. If it be true 

 that all the northern erratics which are scattered over the low 

 grounds of England, Denmark, Holland, Germany, Poland, 

 and Russia, owe their origin to boulder-laden ice carried by 

 ocean -currents, no such warm water as Mr Mackintosh de- 

 siderates could possibly have come from the east or south-east. 

 We are left then to infer that the supposed warm current must 

 have flowed up the Severn valley directly in the face of the 

 CrifTel current, 1 underneath which it suddenly plunged at a 

 high temperature, the line of junction between it and the cold 



1 It must have likewise flowed in more or less direct opposition to the 

 current which, in accordance with the iceberg hypothesis, transported 

 boulders southwards from the high grounds of South Wales ! 



