SOME RIVERS OF CONNECTICUT. 375 



Connecticut at Middletown, where it enters the plateau, 

 and at its mouth, will give some idea of the amount of 

 the warping. It will not give an exact measure of it for several 

 reasons : first, the upper courses of the rivers have not yet 

 reached the present baselevel ; second, the present altitude of 

 the uplands is the result of the post-Cretaceous' uplift and warp- 

 ing, plus a probable later post-Tertiary uplift (to be mentioned 

 later), besides several minor oscillations, the last of which was 

 downward, and is recorded near the coast in the drowned con- 

 dition of the rivers. As has been already said, the peneplain is 

 highest in the northwest, and gradually declines to sea level 

 toward the south and east. 



Consequences of the uplift. The consequences of this uplift 

 are seen in the valleys, which are cut into the peneplain, and 

 which have destroyed the level character of the country. In 

 the hard crystalline rocks the valle_ys are generally narrow and 

 deep, with bold slopes ;^ where they are cut in the crystalline 

 limestone, they are wider and more open. In marked contrast, 

 however, is the lowland on the Triassic area in which only the 

 trap ridges remain to tell of the former altitude of the general 

 surface, and the immense amount of erosion which has taken 

 place on the soft sandstones and shales. Indeed erosion has 

 progressed so rapidly on these soft rocks, that they have been 

 worn down almost to a new baselevel in the same length of time 

 in which the hard crystallines have been only trenched. This fact 

 cannot be too strongly emphasized. The broad sandstone low- 

 land from New Haven north into Massachusetts has been carved 

 out of the uplifted peneplain in soft rocks, during the same time in 

 which the Connecticut has excavated its gorge in the crystallines 

 below Middletown, and the Housatonic has opened its upland 

 valley on the limestones. The difference in results is due not to 



' An exaggerated idea must not be had of the steepness and narrowness of these 

 crystalline valleys. The valley of the Farmington, five miles up from where it opens 

 into the Triassic sandstone, is 400 to 500 feet deep, and a mile and a half wide at the 

 top. The Connecticut valley, just below Middletown, is about 400 feet deep and two 

 miles wide at the top. These are fair representatives of the valleys in the crystalline 

 rocks in the central part of the state. 



