of Secular Changes of Climate. 1 05 



diameter are found in it; and Prof. J. Geikie mentions 

 having seen one four feet in thickness. Stones of this size 

 in a fine laminated clay evidently indicate the presence of 

 floating ice. But, as Prof. J. Geikie remarks, " it is rather 

 the general character of the clays themselves than the 

 presence of erratics which indicates colder climatic con- 

 ditions. The fine tenacious brick-clays are not like the dark 

 sludge and silt which now gather upon the estuarine bed ot 

 the Tay, but resemble and in some cases are identical in 

 character with the laminated clays of true glacial age w r ith 

 Arctic shells." These Carse-clays, as he further remarks, 

 appear in a large measure to be made up of the fine " flour 

 of rock " derived from the grinding action of glaciers which 

 then occupied the Highland valleys, and from which muddy 

 waters escaped in large quantities in summer owing to the 

 melting of the snow and ice. In short, these Carse-clays 

 appear to coincide with the most recent period of local glaciers. 



During that period some of the glaciers, as Prof. J. Greikie 

 has shown, appear to have even reached the sea-level. For 

 example, at the mouth of Glen Brora, in Sutherland, there is 

 a well-marked moraine with large blocks resting upon, and 

 apparently of the same age as, the deposits of the raised 

 beach *. Mr. Robert Chambers also observed moraine matter 

 resting upon the 30-feet beach at the opening of Glen Iorsa, 

 in Arran. In many of the Highland sea-lochs, says Prof. J. 

 Geikie, glaciers appear to have come down to the sea and 

 calved their icebergs there. This, he thinks, is probably the 

 reason why the 40-50-feet beach is not often well seen at the 

 heads of such sea-lochs. The glaciers seem in many cases to 

 have flowed on for some distance into the sea, and thus pre- 

 vented the formation of a beach and cliff-line. 



The greater magnitude and torrential character of the rivers 

 of that period were no doubt due to the melting during 

 summer of great masses of snow and ice. The presence of 

 the large Greenland whale, found frequently in the Carse 

 deposits, would seem to indicate a somewhat colder sea than 

 now surrounds our island. A decrease of temperature of the 

 sea is what would necessarily occur from a slight diminution 

 in the volume of the Gulf- stream, arising from the greater 

 deflection of equatorial water into the southern hemisphere. 



Another circumstance deserves notice here, as it seems to 

 indicate that the climatic conditions of the two hemispheres 

 were at the period of the Carse-clays the reverse of what they 

 are at present. During that period the sea stood higher in 



* i Prehistoric Europe/ p. 411. 



