BUFFALO SOCIETY OF NATURAL SCIENCES 1 83 



if 



proves conclusively that the beds could not have been deposited by 

 an advancing sea, as contended by Macnair and Reid, nor yet in a 

 lake, as Geikie holds. It is not even necessary to point to the red 

 color or to the absence of marine fossils; the thickness and coarseness 

 of the deposits absolutely precludes the possibility of their having 

 been formed in the sea. Macnair and Reid hold that the sea trans- 

 gressed from the south to the north, but in that case, while there 

 might well have been a basal conglomerate a few feet thick, this would 

 inevitably have been succeeded vertically by finer deposits, sands at 

 first and then muds or limestones as the water became deeper, and the 

 zone of coarse near-shore deposits would have advanced pari passu 

 with the transgression of the sea. Thus it would have been impossible 

 for coarse material to have been deposited in southern Scotland in 

 the Upper Eevonic when the sea shore stood two hundred miles to 

 the northwest. Greater obstacles arise if we attempt to have these 

 deposits formed in lakes or epicontinental seas. In Forfarshire, the 



Fig. 18. Section to Explain the Deposition of the Old Red Sandstone in 

 the North of Scotland 

 (After Geikie) 



position of "Lake Caledonia," the estimated thickness given by 

 Hickling is 12,500 feet, including the volcanics, or considerably 

 over 10,000 feet of clastic deposits; in Caithness Geikie estimates 

 the series which he supposed to have been contemporaneously de- 

 posited in "Lake Orcadie" at 16,200 feet. These two lakes were 

 separated by the Crystalline Highlands, a strip of land about 90 miles 

 broad, which apparently supplied the sediments for Lake Orcadie. 

 The waves of this great lake, which is estimated to have had at its 

 maximum a surface of about 48,000 square miles, cut back into this 

 old mountain chain which was at the same time being denuded by the 

 rivers which brought their loads into the lake. In its maximum devel- 

 oped Lake Orcadie extended from Nairn to the Shetland Islands, the 

 Orkneys representing a sublacustrine rise. The cross section made 

 by Geikie is here reproduced in order to show his interpretation 

 (fig. 18). It is at once apparent that there was not enough dry 

 land to supply the thousands of feet of flagstones making up the 

 Caithness series. It is even more difficult to surmise whence came 



