J, W. Stather — Sources of Yorkshire Boulders. 19 



jDvoportionately novtliwards, the figures being 13 per cent, at 

 Dimlingtou and 1 per cent, at Whitby. This northward decrease 

 of the group as a whole is all the more noteworthy when we 

 renaember that the Shap granites and the Cheviot porphyrites, both 

 included in group 4, increase rapidly in the same direction. This 

 seeming anomaly arises, I think, from the influence of the boulders 

 from Scandinavia. x\mong the boulders of South Holderness occur 

 very commonly rocks which agree with certain well-known types 

 of Scandinavia ; of these the best known are the augite-syenite 

 (laurvikite) and the rhomb-porphyry. These types, although not 

 by any means unknown in the drifts of North Yorkshire, are much 

 rarer there than in the south. For instance, at Dimlington one 

 hundred specimens of the Scandinavian rocks above named would 

 be found to one of Shap granite, while, on the other hand, at Robin 

 Hood's Bay or Eunswick Bay (both near Whitby) the Shaps out- 

 number the Norsemen by at least twenty to one. Seeing, then, that 

 the known Scandinavian rocks in group -i are much more common in 

 the south of the county than in the north, and that the distribution 

 of the unidentified rock types included in the same group agrees in 

 this respect with the Scandinavian rocks, I think it may be fairly 

 inferred, tliat these unidentified rocks ai'e probably largely from 

 Scandinavia also. 



Mr. Harker arrived at a similar conclusion when examining 

 Mr. Lamplugh's Flamborough specimens.^ He regarded the bulk 

 of the granitic and gneissic specimens as having been derived 

 either from Scandinavia or from the Scottish Highlands, and 

 remarks : " Among these are some undoubted Norwegian rocks, 

 while none can be pointed out as certainly brought from Scotland. 

 It may be, then, that the whole of the doubtful rocks are also of 

 Norwegian origin." 



It is worthy of note with regard to the smaller boulders and 

 pebbles of the boulder-clay and gravels of East Yorkshire that 

 among these the percentage of the far-travelled rocks is much 

 higher than among the larger boulders. There are certain types 

 also among the smaller specimens which seldom appear as large 

 boulders. Among these is a fairly definite group of rocks, which 

 are known among East Yorkshire collectors as poiyhjrites, and are 

 referred with some confidence to the Cheviot Hills. The evidence 

 in support of this conclusion may be briefly stated as follows : — 

 (1) The erratics seem to match the descriptions of the Cheviot 

 rocks published by Mr. J. J. H. Teall and others. (2) Pebbles of 

 these rocks increase, both in numbers and in size, as we approach 

 the Cheviot district, (o) During a recent excursion (July, 1900) to 

 the Cheviot Hills, arranged by the Yorkshire Geological and Poly- 

 technic Society, many rocks similar to these East Yorkshire erratics 

 were seen in place. 



There is still another note to be made with regard to the Cheviot 

 boulders, and that refers to their vertical distribution. I think it 

 will be found, that the Cheviot rocks are more plentiful in the 

 1 Proc. Yorkshire Geol. and Polytcch. Soc, vol. xi, pt. 3, p. -109. 



