l6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



the geologic structure is the fundamental factor which controls 

 the nature of the surface. 



The Central Lowland is in its larger aspect a plain,- but in 

 detail it is seen to consist largely of low hills with flowing out- 

 line. The rivers meander through the Lowland in broad valleys 

 but with well-defined channels. 'Prominent but interrupted ridges 

 of trap rock run the length of the Lowland and rise several hun- 

 dred feet above the general level. The principal streams are 

 less than a hundred feet above the sea, but the rolling surface of 

 the Lowland lies mostly from 100 to 400 feet higher, the northern 

 parts in Connecticut averaging about 100 feet higher than the 

 southern. The gentle slopes and deep soil are suited to agricul- 

 ture; numerous small cities and several larger ones have developed 

 and communication is easy in all directions. 



The Lowland plain bevels the strata of the rocks beneath and 

 is therefore a plain of erosion. But, even if the present narrow 

 river valleys be in imagination refilled with the rock which the 

 streams have excavated, the Lowland surface will be seen to be 

 not level, but diversified by low hills 100 to 200 feet in height. 

 It is therefore not a plain but a peneplain ; that is, almost a plain. 

 The general uniformity of level at an elevation which in central 

 Connecticut averages about 200 feet, indicates, furthermore, that 

 the peneplain was developed by subaerial erosion when the land 

 stood about 200 feet lower than at present. A more recent uplift 

 has permitted the streams to cut to a lower level, and erosion has 

 begun to destroy the peneplain which formerly it brought into 

 existence, by beginning to create a new one at the present level 

 of the rivers. 



The Eastern and Western Highlands are in their larger 

 aspects plateaus, and in regions removed from the principal rivers, 

 as at Litchfield, this relative flatness of the upper surface is con- 

 spicuous, the local relief being no greater than in the Central 

 Lowland, though the average elevation may be more than a 

 thousand feet above the sea. Over most of the highland area, 

 however, the rivers and their tributaries have sunk into the 

 upland, eroding narrow valleys of considerable grade, dissecting 

 the plateau into a greater or less ruggedness, and making com- 

 munication across the drainage systems more difficult than in the 

 Lowland. If the valleys be filled in imagination with the rock 

 which the rivers have removed from them, the plateau character 



