550 W. M. DAVIS DATES OK TOPOGRAPHIC FORMS. 



away toward the west. Looking from its edge eastward, the trap-ridges of 

 the Connecticut valley are seen rising to about the same height as the plateau, 

 and beyond them portions of the corresponding eastern crystalline plateau 

 may be seen, still closely accordant with the same general scale of elevation. 

 The valleys and lowlands by which the plateau is interrupted may be filled 

 again in imagination to the general level of its surface, and we shall have 

 then restored a part of one of the more important elements, if not the most 

 important element, in the topography of the Atlantic slope. The restored 

 surface is not by any means perfectly even ; but its inequalities are moder- 

 ate, and it may be justly called a peneplain. It is manifestly a surface of 

 denudation, for it is not at all in sympathy with the disordered structure of 

 the crystallines or with the faulted monocline of the Triassic area. It is 

 manifestly a surface of long-enduring denudation at about the same altitude 

 of the laud, for otherwise it could not have been reduced to so nearly level 

 a surface as its parts now show its whole to have been before the present 

 valleys were sunk into it. It is manifestly a product of denudation, not at 

 the present altitude of the laud, but when the whole region stood at a less 

 altitude, such as would place the surface of the old peneplain close to base- 

 level.* The form, extension, and date of completion of the peneplain, the 

 date of its elevation to its present altitude, the tilting it may have suffered 

 in elevation, and the time during which the valleys that now break it have 

 been excavated, are to be examined. 



The form of the peneplain may be seen from any one of the many slightly 

 higher points of its upland surface. For example, taking the Air Line 

 railroad eastward from Middletown, Connecticut f (see figure 1), one soon 

 passes from the open Triassic lowland to the narrower valleys that are cut 

 in the harder crystalline rocks of the eastern plateau ; and at the little 

 station of Cobalt, a road toward the north leads to Cobalt hill. The hill 

 consists of a hard quartzitic schist, and affords a fine prospect over the sur- 

 rounding country toward the east, south, and west. The prevailing feature 

 of the view is the general evenness of the uplands. There are no summits 

 rising like mountain peaks above the general level. The valleys that are 

 cut below^ it will be referred to in a later paragraph. If an excursion be 

 made eastward from Springfield, Massachusetts, to the hills of the plateau 

 back of Wilbraham, the evenness of the upland is less marked ; a number 



*See the Topographic Development of the Triassic Formation of the Connecticut Valley, by W. 

 M. Davis: Amer. Journ. Science, 3d ser., vol xxxvii, 1889, pp. 423-434. 



fThe various towns, rivers, and geogiaphic districts mentioned in this paper are indicated by 

 initial letters on several rough diagrams. The last pages of the essay contain an index ot names 

 and abbrevations employed. The diagrams have been prepared in the hooe that they might serve 

 a useful purpose to ihose readers who are not familiar with the details of the region under con- 

 sideration, for my own experience in reading has shown me that geological arguments of relative 

 simplicity are often obscured by the geographical integument that encloses them. The atlases in 

 common use generally fail to locate small towns and streams; special maps of state surveys are 

 often difficult to examine, as they present much more than is wanted. A good map, especially 

 prepared for this paper, would be too expensive. Diagrams are therefore attempted, somewhat 

 experimentally. 



