HowartJi : The Ice-borne Boulders of Yorkshire. 145 



Western group of rocks reached Yorkshire. Rocks north of 

 that hne travelled to Yorkshire by the Stainmoor and Tees 

 route. There are, however, a few exceptions to this general 

 rule. Eskdale granite, for example, has been recorded north 

 of this line, whereas its general distribution is southward of 

 its outcrop. Similarly Shap granite, the outcrop of which 

 is north of this suggested line, is distributed far to the south- 

 west. These dispersals were probably in the earlier stages, 

 when the local glaciers had free outlets. 



It should be remembered that these rocks are everywhere 

 accompanied by others picked up all along the route, and, of 

 course, in the mid and terminal stages, greath^ exceeding them 

 in numbers. For instance, the Western group is accompanied 

 by great numbers of boulders of Carboniferous Limestones, 

 Sandstones, Cherts, etc., and the same rule applies to the 

 Northern group, to be mentioned presently, v/hich are accom- 

 panied by greywacke sandstones and conglomerates, Magnesian 

 limestone of the Roker type, etc. 



THE NORTHERN GROUP. 



Rocks from Durham County, the Cheviot area of Northum- 

 berland, and Scotland are present in the Yorkshire drift. 



These include andesites and porphyrites from the Cheviots, 

 probablv both from the English and Scottish side, but the 

 former predominating ; the characteristic ' Haggi- ' rock from 

 the northern edge of the southern uplands of Scotland ; red 

 jasper, sanidine trachj^te, dolerites and basalts from the southern 

 uplands of Scotland ; and Silurian grits from the Valley of the 

 Tweed. There are also records of certain Highland Schists 

 from as far north as the Ochill Hills in Perthshire. 



These rocks seem to have been first carried out to sea in 

 south-eaiit Scotland, east Northumberland and Durham, and to 

 have been deflected southwards by the Scandinavian ice-sheet, 

 as the Tees glacier and its contents were. 



Porphyrites of the Cheviot type are the most abundant, 

 and are everywhere along the Yorkshire coast, and further 

 south into Cambridgeshire. They are found also in many 

 localities inland, including Barton-on-Humber, about Beverley, 

 at Seamer, at Wykeham, in the Vale of Pickering, in Yedman- 

 dale, at Goathland, at Carlton Bank, Bold Venture, Scarth 

 Nick, Thirsk, and Upsal (Hag's Hill). They range from sea- 

 level up to 950 feet, O.D. 



The fact that they are found among the highest drift 



1908 April I. 



K 



