214 Prof^ T. Rupert Jones — South Wales Entomostraca. 



extravagant allowance for the additional depth gained on this account, 

 still there could not possibly be water sufficiently deep to float a glacier 

 of one or two thousand feet in thickness. The North Sea would have 

 required to be nearly ten times deeper than it is at present to have 

 floated the ice of the Glacial period. The mass und«r which, as we 

 have seen, the Ochils were then buried, if placed in the centre of that 

 sea, would still have its upper surface as high above the sea level as the 

 tops of our Pentlands. We may conclude, with the most perfect cer- 

 tainty, that the ice entering the North Sea from the east of Scotland 

 must have continued its course in one unbroken mass till it reached 

 the deep water of the Atlantic, to the west of the Orkney and Shet- 

 land Islands. It is hardly necessary to remark that the waters of 

 the North 'Sea would have but little effect in melting the ice. A 

 shallow sea like this, into which large masses of ice were entering, 

 would be kept constantly about the freezing point, and ice-cold 

 water has but little melting power. It takes 14:21bs. of water, at 

 33° of temperature, to melt one pound of ice. In fact, an icy sea 

 tends rather to protect the ice entering it from being melted than 

 otherwise. And besides, owing to fresh acquisitions of snow, the 

 iee-gheet would be accumulating more rapidly upon its upper surface 

 than it would be melting at its lower surface, supposing there were 

 sea-water under that surface. The ice of Scotland during the 

 glacial period must, of necessity, have found its way into warmer 

 water than that of the North Sea before it could have been melted. 

 But this it could not do without reaching the Atlantic, and in getting 

 there it would have to pass round by the Orkney Islands, along the 

 bed of the North Sea, as land-ice. 



This will explain how the Orkney Islands may have been glaciated 

 by land-ice; but it does not, however, explain how Caithness should 

 have been glaciated by that means. These islands lay in the very 

 track of the ice on its way to the Atlantic, and could hardly escape 

 being overridden ; but Caithness lay considerably to the left of the 

 path which we would expect the ice to have taken. Tho ice would 

 not leave its channel, turn to the left, and ascend over upon Caithness 

 unless it were forced to do so. What, then, compelled tiie ice to 

 pass over Caithness ? 



( Jb he concluded in the June Number.) 



VI. — On soiviE BivALVED Entomosteaca from the Coal-measukks 

 OF South Wales. 



By Prof. T. Eupert Jones, F.G.S. 



(PLATE IX.) 



IN the spring of 1869 Mr. William Adams, F.G.S., of Cardiff, sent 

 to me for examination several pieces of Coal -shale, bearing some 

 minute organisms which had been recognized as Entomostraca by 

 Mr. Charles Moore, F.G.S. The shale, in some of its layers, which 

 are more or less bituminous, is full of Anthracomya Phillijasii, 



