Physical Geography. 1 1 7 



mountains, and on the banks, and perhaps as occasional 

 islands, volcanic cones disgorged streams of lava and 

 discharged showers of ashes and stones, to be interstrati- 

 fied with the ordinary sediments, in a manner analogous 

 to that which accompanied the deposition of the Miocene 

 strata in Auvergne and other areas in what is now 

 central France. At the same time, from the lofty moun- 

 tains that now form the Highlands, but higher then, 

 glaciers descended into the water, and fleets of icebergs 

 floated hither and thither, and, melting, dropped their 

 moraine matter to intermingle with other sediments, 

 while further south, in Cumbria, similar glaciers de- 

 scended from the ancient mountains, higher and dif- 

 ferent in form from those of modern date in the same 

 area. 



In a region still further south, we come to the 

 lake in which the Old Eed Sandstone of South Wales 

 and the adjoining counties was deposited. These 

 strata certainly spread further north and west than the 

 edge of the main mass does now, a fact shown by the 

 large outliers by Presteign, Clun, and Bettws Crwyn in 

 Montgomeryshire. Making an allowance for this ex- 

 tension, the lake must have been not less than about 

 100 miles in length, by a breadth varying from 70 to 

 100 miles, for traces of Old Eed Sandstone have been 

 proved in deep borings through the coal-measures at 

 the south end of the South Staffordshire coal-field. 

 Away in the distant west, rose the lofty mountains 

 formed in part of the far more ancient Lower Silurian 

 rocks of North Wales, but no contemporaneous volcanic 

 rocks are anywhere found among the Old Red Sandstone 

 strata that were deposited in the adjacent lake, the 

 eastern shores of which were, I think, low and unim- 

 posing. 



