430 W. 3L Davis — Topographic Development of the 



time enough lias already been allowed, and that the strong- 

 Jurassic topography was really worn out somewhere in Creta- 

 ceous time, when all this part of the country was reduced to a 

 nearly featureless plain, a " peneplain" as I would call it, at 

 a low level ; a plain that was broadly uplifted in early Tertiary 

 time — or thereabouts — and thus thrown into another cycle of 

 destructive development, and whose elevated remnants are 

 now to be recognized in the crystalline uplands on either side 

 of the present Triassic valley of Connecticut and Massachusetts 

 (Emerson), and in the crest-line summits of the main trap 

 ridges. The general equality of upland altitude on very diverse 

 structures is the essential argument for the base-leveling of the 

 region ; but it is not intended to discuss this in detail at 

 present. The post-cretaceous elevation that lifted the ancient 

 lowlands was greater in the interior than near the coast, and 

 our present valleys are deeply sunk and broadly opened in it. 

 An extension of the same ancient lowland, now similarly ele- 

 vated and dissected, is to be found in northern New Jersey. 

 Standing on a commanding point of view, such as the fine 

 drumlin a mile or more southeast of Meriden, whence the main 

 trap ridges may be seen for many miles north and south, one 

 must in imagination refill the low ground with the shales, 

 sandstones and conglomerates that have been worn away, and 

 thus raise the surface up to the level of the main trap ridges, 

 or even a little higher, in order to perceive the form attained 

 by the land in the late stage of the degradation of the dislo- 

 cated Triassic blocks, when all this region stood lower. It 

 was only after the close of this first cycle of degradation and 

 after the elevation of the country to something like its actual 

 altitude at a later date that the beginning of the present or 

 second cycle of valley-making was reached. Some unmeasured 

 part of the Tertiary and later time has been allowed for this 

 part of the work. In the crystalline rocks, the valleys are 

 narrow and steep sided, as is so finely shown in the expressive 

 topographic map-sheets of western Massachusetts ; but in the 

 Triassic area, where the sandstones are relatively soft, the 

 valleys have been widened out into broad lowlands, only the 

 thicker trap-sheets retaining still some indication of their 

 former altitude. The latest touches have been given to their 

 form by glacial action, both destructive and constructive, as 

 well as by river deposits in the valley bottoms and by estuary 

 deposits in the coastal districts. Except in terrace and gorge 

 cutting, post-glacial erosion is insignificant. If this sketch be 

 correct, we may conclude that the present topography is not 

 an immediate product of erosion on the Jurassic deformations 

 of the Triassic beds ; it is an uncompleted advance in a second 

 cycle of development, with recent complications by glacial ac- 



