Messrs Peach and Home on the Glaciation of Caithness. 319 



drift on the grits and conglomerates towards Dunbeath and 

 Berriedale, coupled with the overlap of a reddish-brown 

 boulder clay on the Caithness flags at Eeay. We shall point 

 out presently, however, that these features are satisfactorily 

 accounted for by supposing that the ice came from the south- 

 east. We shall have occasion to point out also that this 

 supposed movement from the north-west is at variance with 

 some facts recently brought to light regarding the direction of 

 the ice-markings and the dispersal of the stones in the 

 boulder clay, while it leaves unexplained the occurrence of 

 various secondary rocks in that deposit. Mr Jamieson 

 inferred that the shelly boulder clay of Caithness w^as of more 

 recent date than the lower boulder clay of Scotland, which is 

 usually unfossiliferous, being led to this conclusion by the 

 small proportion of Arctic forms in the fauna of that 

 deposit. 



In 1870, our colleague, Dr Croll, contributed an article to 

 the Geological Magazine* in which he disputed the marine 

 origin of the Caithness boulder clay, regarding it as a product 

 of land ice. He called attention to two points noted by pre- 

 vious writers on the subject : first, that with the exception 

 of the organic remains, this deposit closely resembles the 

 ordinary boulder clay of Scotland, which is generally ascribed 

 to the action of land ice ; and, second, that the marine shells 

 are scattered irregularly through the deposit, and are smoothed 

 and striated precisely like the stones in the boulder clay. 

 He argued that the presence of these organic remains does 

 not necessarily prove the marine origin of the till, but rather 

 that they had been borne inland with the moraine profonde 

 from the bed of the Moray Firth and the North Sea. He 

 endeavoured to explain the origin of the shelly boulder clay 

 by supposing that the Scotch ice which filled the basin of 

 the Moray Firth was deflected by reason of the Scandinavian 

 mer de glace, and was compelled to overflow the Caithness 

 plain. In his volume on " Climate and Time,"-(- he quotes 

 the testimony of one of the authors of this paper in proof of 

 the gradual bending round of the Scotch land ice between 



* Geol. Mag., 1870, pp. 209-271. 

 t "Climate aud Time," p. 453. 



