The Scottish Naturalist. 245 



invasion is proved not only by the direction followed by stones 

 of local derivation, and by boulders which have come south 

 from Scotland and the northern counties, but by the occurrence 

 in the boulder-clay at Cornelian Bay and Holderness of erratics 

 of certain well-known Norwegian rocks, which have been recog- 

 nised by Mr Amund Helland. The occurrence of chalk-flints 

 and fragments of Oolitic rocks in the neighbourhoods mentioned 

 by Mr Mackintosh, thus only affords additional evidence in 

 favour of the land-ice origin of the drift-deposits described by 

 him. The mer de glace that flowed down the east coast of Eng- 

 land seems to have encroached more and more upon the land, 

 until eventually it swept over the low-lying Midlands in a south- 

 westerly direction, and coalesced with the mer de glace that 

 streamed inland from the basin of the Irish Sea, and the ice that 

 flowed outwards from the high grounds of Wales. The united 

 ice-stream would thereafter continue on its south-westerly course 

 down the Severn valley to the British Channel. I have no 

 doubt that Mr Mackintosh will yet chronicle the occurrence of 

 chalk-flints and other eastern erratics from localities much further 

 to the south than Ledbury. 



Again, considerable stress has been laid by Mr Mackintosh 

 upon the occurrence of chalk-flints in the drift-deposits of Black- 

 pool, Dawpool, Parkgate, Halkin Mountain, Wrexham, the 

 peninsula of Wirral, Runcorn, Delamere, Crewe, Leylands, 

 Piethorne (near Rochdale), and other places. "All these flints," 

 Mr Mackintosh remarks, "belong to the basin of the Irish Sea, 

 and have almost certainly crossed the general course of the 

 northern boulders on their way from Ireland." Here, unfortu- 

 natelv, the Irish Sea intervenes to conceal the evidence that is 

 needed to enable us to track the exact path followed by the 

 erratics in question. I am not so certain as Mr Mackintosh 

 that the chalk flints he refers to came from the north of Ireland. 

 Chalk-flints occur pretty numerously in the drift-deposits in the 

 maritime districts of north-eastern Scotland, which we have every 

 reason to believe have been derived from an area of Cretaceous 

 rocks covering the bottom of the adjacent sea ; and for aught one 

 can say to the contrary, patches of chalk-with-flints may occur in 

 like manner in the bed of the Irish Sea. I cannot at present 

 remember whether any boulders of the basalt-rocks, which are 

 associated with the chalk in the north of Ireland, have been 

 recognised in the drifts of the west of England ; but if the chalk- 

 flints really came from Antrim, it is more than probable that they 



