■i8g 3 . SHELLY-SANDS AND GRAVELS. 427 



'.Latter-day geologists coming from the study of glacial deposits in other 



-countries have felt difficulties in accepting this explanation. They 

 have found that an ice-sheet comparable to that of Greenland of the 

 present day best explains the phenomena in the countries in which 

 they have studied the glacial drift, and they seek to apply the same 

 explanations to the Drift of the British Isles. The low-level drifts 

 are more easily dealt with on this hypothesis than the high-level, but 

 as they are essentially of the same nature, it seems necessary for 



■consistency' sake to apply the same explanation to both. There are 

 also certain phenomena which are thought to be inconsistent with the 

 submergence theory, one of them being the position of boulders 

 at a level higher than the parent rocks from which they were 



-derived. 



Again, it is said that the high-level drift is very partial and 

 sporadic in distribution, that there is no marine drift in the interior 

 mountain valleys, that there are no raised beaches, that the shells are 

 always broken as if a heavy body had moved over them, that they 

 occur mixed in species in a way that never happens in nature ; that 

 the two valves of bivalves are never found united — that they never 

 occur in any bed as if the molluscs had lived on the spot, and finally, 

 the species characteristic of warmer climates are mixed with those of 

 colder climes, such as never occur together in the sea at the present 

 day. Furthermore, the advocates of submergence are asked to 

 produce stones from the Drift with the remains of barnacles or other 

 organisms upon them. 



It is also roundly asserted that 'rocks have never been found 

 north of their origin, and by implication never will be. It is also 

 suggested that, if the sea has flowed over the land to such a depth as 

 the submergers require, deep-sea beds or beds of some sort containing 

 sea-shells in situ, like what we find in the so-called Clyde Beds, should 

 be common, whereas they do not exist. 



The shading off of the glacial deposits southward is also looked 

 upon as consistent with a land-ice, and inconsistent with a sea-borne 

 origin. 5 These are what we may classify as objections founded upon 

 observation. I think I have catalogued the greater number, but if 

 any are omitted I have not the least doubt that I shall be reminded 

 of them. In the meantime, we will consider another class of objections 

 that are physical and theoretical. The subsidence of this solid land 

 without evidence of volcanic action seems to some minds so impro- 

 bable as to demand the clearest and fullest proofs before it can be 

 admitted. The worst is, that when one condition is satisfied and paid 



'What are called striated pavements, in which the striae in the boulders are 

 . approximately parallel, are pointed to as evidence of the passage of an ice-sheet. 

 These are, however, only found, so far as I know, at low-levels in the Boulder Clay. 

 It is considered that floating ice could not have affected the boulders in this way. I 

 do not propose to examine now the further question of bed-rock striation which is a 

 much wider one than the origin of the Marine Drift. 



