22 Proceedings of the Royal Physical Society. 



the Forth and Clyde ; but this peculiar feature may be satis- 

 factorily accounted for. The fossils found in the Caithness 

 deposit represent the fauna that had lived and died on our 

 shores before the advent of the glacial period, while those in 

 the Forth and Clyde beds belong to the 100 feet sea-beach. 

 The latter represent the Arctic species that approached our 

 shores after the climax of glacial cold, when the ice retired 

 from the shallow seas to the interior of the country, the water 

 in the various fiords being kept at a low temperature by the 

 melting of the inland ice. During the climax of the cold 

 period represented by our boulder-clays, the ice-front was so 

 far out to sea, that no marine organisms could reach our 

 present shore-line. When the ice had completely disappeared, 

 owing to the gradual amelioration of climatic conditions, the 

 old denizens of our shallow seas returned again to their former 

 haunts, while the Arctic forms migrated to the bottom of our 

 deepest sea lochs, or vanished from our islands altogether. 



On the south side of the Moray Firth there are beds con- 

 taining shells in the position in which they lived and died. 

 Intercalated between two boulder-clays, these deposits point 

 to a warm inter-glacial period, when the ice must have 

 retreated far into the interior of the country, and when the 

 land was submerged to a depth of about 500 feet. When the 

 relations of these beds, now being studied by several glacial- 

 ists, are made known, I have no doubt that another interest- 

 ing chapter will be added to the history of the glacial period. 



In conclusion, I wish to refer again to the crystalline rocks 

 of the Highlands, because it seems to me that the origin of 

 these crystalline schists forms the great question of the im- 

 mediate future among Scottish geologists. There cannot be 

 the slightest doubt that the recent researches in the north- 

 Avest of Sutherlandshire demonstrate that crystalline and 

 sedimentary rocks have been converted into schists, and they 

 enable us to follow the processes by means of which these 

 changes have been effected. With reference to the Central 

 Highlands, it is highly probable that the metamorphic rocks 

 of sedimentary origin may yet yield fossils at certain locali- 

 ties. From the manner in which their component particles 

 have been made to move over each other, owing to the enor- 



