172 S. V. Wood, Jun. — Ilej:^!!/ to Mr. James Oeikie. 



Bridlington fauna, moreover, is peculiarly Arctic and North American, 

 which is not the case with that of the Lower or Middle Glacial 

 sands ; ^ showing that the cold came on quicker than the mollusca 

 could migrate with it. 



Now, in the face of this, what are the pretensions to antiquity of 

 the Scotch Till ? Some intercalated beds of gravel, sand, mud, and 

 clay, it is said. But intercalations of gravel, sand, and mud, occur 

 in all Glacial clays, whatever be their age ; and the Bridlington bed 

 itself is merely a sandy intercalation in the body of the Purple clay, 

 the Yorkshire coast showing many such. If the unfossilifefous 

 character of the Scotch Till be relied on, I reply that this can be no 

 ground to support the correlation claimed, but merely one that can 

 be urged against its correlation with any other deposit. The 

 Caithness Clay, however, is fossiliferous, and it has not been shown 

 that this clay is distinct in age from the Scotch Till.- Mr. Croll 

 did, indeed, attempt to show that it was the bed of some distant 

 part of the North Sea, shoved into Caithness by an ice-sheet press- 

 ing down from Scandinavia, and filling the North Sea during the 

 period of the Scotch Till ; but if such were the case (which, how- 

 ever, I dispute), that would not remove the Caithness clay to a later 

 period than the Scotch Till ; for the fauna of this clay would 

 either be that of the period of the Till, or of the immediately pre- 

 ceding period. Now the fauna of the Caithness clay, as obtained by 

 Mr. Peach, and identified by Mr. Gwyn Jeffreys, comprises 66 forms 

 of mollusca, of which 12 have not occurred in any part of the Crag ; 

 but the whole of which 66 occur as living, and living, moreover, on 

 this side of the North American continent. The molluscan forms of 

 the rest of the beds, both of the East and of the West side of Scotland 

 (all of which are said to rest on the Till), are about 90 in number,^ and 

 all still living on this side of the North American continent, a con- 

 siderable arctic facies pertaining to some of them ; and of these no 

 less than 26 are unknown in any part of the Crag, showing a yet 

 greater departure from the Crag fauna, in accordance with their 

 admittedly newer position of superiority to the Till. It cannot be 

 urged that the affinity of the East Anglian beds with the Crag is 



^ The Middle Glacial fauna, however, affords indications of the incoming of this 

 North American character in the occurrence of Venus Jluctuosa, a Bridlington and 

 North American shell not known in the Crag. 



^ Mr. Harmer and I examined the Scotch heds on the one side of the Highlands up 

 to Cromarty, and on the other down to Glasgow. Of course, our examination was 

 only a hasty and superficial one ; but we could see nothing beyond the difference in 

 the constituent material, due to the different character of the rock masses of the two 

 areas, to separate the Boulder-clay of Cromarty from the Till of the region west of 

 Glasgow. If I am- not mistaken, the Cromarty clay is merely a continuation of 

 the Clay of Caithness, and passes up into the Highland boulder sands about the 

 Northern end of the Caledonian Canal, as the Till does beyond the Southern end. 



^ A larger number than 90 have been reported from these beds ; but Mr. James 

 Smith's lists are not trustworthy. I have taken my result from the revision of Mr. 

 Smith's authorities, made by Mr. Crosskey, with the assistance of Mr. Jeffreys. If 

 the other (unauthenticated) shells mentioned by Mr. Smith be added, however, the 

 fauna would not be altered at all in character, nor the proportion of it occui-ring in 

 the Crag be materially varied. 



