6 (.KEEN MOUNTAINS IN MASSACHUSETTS. 



setts, the Berkshire valley. This valley lias a floor of crystalline limestone, 

 often a saccharoidal marble of Cambrian and Lower Silurian age, on which 

 stand Long island-like ridges of schist, of Lower Silurian age, and it extends 

 with a breadth of several miles from northern Vermont to Alabama. The 

 schist is everywhere underlain by the limestone, which is marked by 

 the fertility of its soil ; and, along its whole length, its wealth of limonite 

 ores has for more than a century formed the basis of important iron indus- 

 tries. In the folded strata of this valley belt in Vermont and Massachusetts, 

 subsequent erosion has left island-like mountains, sometimes of anticlinal, 

 but generally of synclinal structure, with more or less pitch in their axes. 

 Instances of the latter are Lolus (Dorset), Anthony, Grreylock, Everett, 

 etc., rising to 1,500 or 3,000 feet above the valley, and surrounded to a 

 greater or less height above the base by the limestone, and heavily capped 

 with the weather-resisting schist. Instances of anticlinal structure are the 

 less elevated pine hill near Rutland and the ridge which connects it with 

 Danby hill in Vermont. 



On the west, this limestone valley has for a wall the Taconic moun- 

 tains, with peaks rising 1,500 to 2,500 feet above the valley. This is a 

 synclinal range of the same Lower Silurian schist, but, having its trough 

 at a lower level, the limestone foundation appears only at the base. 



Turning now to the region east of the axis of the Green mountain 

 anticline, we find no great and continuous depression comparable to that of 

 the valley of Vermont until we reach the Connecticut valley ; and this is 

 occupied by much later strata — Triassic resting on Devonian. This eastern 

 region is a very roughly mountainous mass of schist, and, though of plateau 

 origin, is crossed by deeply cut transverse valleys, which receive longi- 

 tudinal tributaries, whose courses are determined in the main by the 

 geologic structure of the territory. All alongthe eastern edge of the axial 

 belt of the mountains there occur such narrow, longitudinal valleys, and 

 as they contain, more or less continuously, beds of limestone of either 

 ( iambrian or Lower Silurian aye, they define the eastern limit of the Green 

 mountain range proper, with less topographic but with equal geologic 

 sharpness. 



