Shells of the Holdemess Basement Clays. 137 



experience in Greenland that such streams deposited a muddy 

 sediment, averaging 3 inches yearly upon the sea bottom into 

 which it flowed and incorporating in its body the shells and 

 stones already present on its floor. 



The shells in the streaks and pockets of sand imbedded at 

 different levels in the body of the clay, appear to have a 

 different origin although of the same geological age, and as 

 I suggest came into our area from a distant region near to, or 

 within the Arctic circle, brought by floating ice in some form, 

 liftea from the sandy bottom or sea shore by anchor ice, and 

 transported in bulk as frozen masses, or boulders to the York- 

 shire coast. Once deposited, the frozen sand would lose 

 cohesion and easily acted upon and distributed. As Mr. Lamp- 

 lugh sa\s, 'Somewhere there must have been a peiiod when 

 the sea was crowded with icebergs and floe ice flowing hither 

 and thither at the mercy of wind and waves., and there is no 

 reason why portions of a sea bottom may not be caught up 

 and carried by detached bergs till stranded on opposite and 

 far distant shores.' 



It is to some such agency rather than to the passage of ice 

 traversing the sea bottom that I think we must look to account 

 for the arctic shells in such abundance. It is significant that no 

 similar assemblage of species occurs living south of the arctic 

 circle, as at present recorded unless at extreme depths. 



The undoubted presence of Bear, and the traces of a fresh- 

 water plant bed, with Limnaea peregra in the basement clay 

 below the purple clay, lends support to the suggested proximity 

 of land ; and this view seems to harmonize with Mr. Lamplugh's 

 opinion ' that the Basement Clay cannot be marine, and can 

 scarcely be other than the product of land ice,' and yet allow 

 for the presence of marine shells in the clay. 



Concerning the place in time of the Bridlington group, Mr. 

 Lamplugh suggests that the old Sea-beach series at Sewerby, 

 below the basement clay is coequal with the Leda myalis bed 

 of the Cromer Cliff, Norfolk. I would go farther, and make 

 the Sewerby shore and the Weybourne Crag march together 

 and place the overlying myalis bed at Runton Gap, the Chilles- 

 ford sand and clay seen at Chillesford Church pit, Suffolk, and 

 the Bridlington beds on the same horizon, as I agree with Prof. 

 Prestwich, Geology, Vol. II., p. 447, 1888 'that' the Bridlington 

 Clay may represent or be equivalent to the more arctic portion 

 of the Chillesford Clay. 



The Chillesford shells in the accompanying list, were 

 collected by Dr. Boswell and myself during 1913, and the 

 myalis species are taken from Mr. Reid. Plioc. Dep. Great 

 Britain (Mem. Geol. Survey), p. 193. Except Lucina borealis 

 all these occur at Bridlington, and like the shells there are 

 frequently found double and in their natural life-positions. 



1917 April 1. 



