The Ash Bed at Meriden. 27 



be found in southern Oregon, where the ditlocalions are of a type 

 very similar to those of the Connecticut valley, but where the date 

 of dislocation is so recent that there has not yet been time to pro- 

 duce much change in the constructional form. Meriden readers 

 should not fail to study the excellent description of this remarkable 

 western region, as presented by Russell in the Third Annual Report 

 of the United States Geological Survey; it has a distinct bearing on 

 the early history of their own country. 



But the date of the dislocation in the Connecticut valley is remote. 

 Time enough has since then passed to allow the erosive forces to 

 smooth down the whole irregular surface of the broken blocks and 

 reduce their original mountainous form to wiiat has been called a 

 plain of base-level denudation; that is, to a surface of moderate 

 relief, worn down to the level of the standing waters into which the 

 streams discharged. This was accomplished long ago, when the 

 land mass stood lower than it does at present, and the old base-level 

 plain is now to be seen only in such remnants as the elevated pla- 

 teau of the crystalline rocks on either side of the valley and in the 

 crest-lines of the higher trap ridges. For in consequence of the 

 elevation that the old plain suffered at some time when its base-lev- 

 elling was well advanced, it has since been again attacked by ero- 

 sive forces, and is now on its way to be again reduced to a lower 

 base-level plain; but time enough has not yet elapsed to allow 

 the completion of this second cycle of work. The work is pretty 

 well advanced on the softer rocks, such as the sandstones, but the 

 crest-lines of the thicker trap sheets are as yet not much reduced 

 below the level of the earlier base-level, and the great mass of hard 

 crystalline rocks on either side of the Triassic belt is very slightly 

 consumed except along the valley lines, where the fastest cutting 

 is always done at first. 



Now in order to understand the present topography, the reader 

 must make a purely geometrical effort; he must picture the series of 

 beds of sandstones and traps, broken into long, narrow blocks and 

 tilted over, and reduced by erosion to a surface of very moderate 

 relief, a base-level plain; and on this plain he must perceive that 

 according to the amount of dislocation of the blocks and the amount 

 of inclination given to their beds, any given member of the series, 

 as the heavy sheet of trap already described in Lamentation Mount- 

 ain, will appear in various outcrop lines. If there be any difficulty 

 in understanding this, let the structure be imitated by laying a num 

 ber of books of different breadths but of the same thickness beside 

 each other, these representing the Triassic series in its original un- 



