64 PALEOZOIC TIME. [CHAP. V. 



In the tracts which were covered by the sea there was 

 continuous deposition throughout the period, but in the 

 lacustrine areas it appears to have ceased altogether for a 

 time ; there is a great gap between the Lower and Upper 

 Old Eed Sandstone, and we have no records of the inter- 

 vening time. But this very absence of deposits is in itself 

 evidence of the conditions which prevailed the lakes must 

 have been dried up and converted into land surfaces, pro- 

 bably in consequence of the continued elevation of the 

 country, and the deepening of the river channels which 

 would result from this elevation. 



We may, therefore, conclude that the general succession 

 of events in the northern areas was as follows : at the 

 beginning of the period the upheaval of the ridges which 

 subsequently became mountain ranges contracted the sea- 

 space into gulfs, which were gradually shallowed by the 

 material poured into them from the land on either side, 

 and by the continued upheaval of the country, till they 

 were entirely isolated from the sea, and were converted 

 into large freshwater lakes, comparable to those of modern 

 North America, and tenanted by a great variety of curious 

 fish. Lake Caledonia must, indeed, have greatly resembled 

 Lake Michigan, which has a length of 345 miles, and an 

 extreme width of only 84 miles. Now the Scottish portion 

 of Lake Caledonia has a length of 160 miles ; and if, as 

 Professor Hull supposes, it stretched continuously into 

 North Ireland, we must add another 80 miles to its western 

 extension, giving a total of 240 miles, while how far it ex- 

 tended to the east of Scotland we have no means of know- 

 ing, but it may well have been 300 miles in length, and 

 its extreme width was perhaps not more than 80 or 90 

 miles. The greater part of Lake Orcadie lay outside the 

 present limits of Scotland, and in that part of the continent 

 which stretched toward Scandinavia, so that we can form 

 no idea of its size. The other lakes seem to have been 



