70 BULLETIN OF THE 



clinal series. A little preparatory consideration of the area! topography 

 of several blocks, Fig. 9, bounded by faults similar to the one in the 

 reservoir valley, will be of service. Each block, consisting of a mono- 

 clinal sequence of harder and softer beds, such as has already been 

 described as the result of the first day's walk, will possess its anterior, 

 main, and posterior trap ridges, with several intermediate and associated 

 ridges and valleys of sandstone and shale, in definite order. The ridges 

 formed on the successive beds will end without apparent cause on the 

 oblique fault lines that bou»id the blocks. If a block be narrow, a 

 quarter to a half a mile wide, for example, the posterior trap ridge will 

 have its south end to the north of the north end of the anterior ridge. 

 At first sight, these two members of the block-sequence would not seem 

 to belong together. Continuity in the monocline can therefoi-e be 

 found only by crossing the country within the limits of a single block, 

 and advancing parallel to its enclosing faults. A cross-section made at 

 right angles to the strike of the beds would soon traverse a fault line, 

 and would only confuse the observei*. This principle is all-important in 

 deciphering the topography and structure of the region. Eeference to 

 Fig. 2 will show that the section there made was traced out obliquely 

 for this reason, although no mention of it was made at the time. 



The fact that there has been a long period (probably Jurassic and 

 Cretaceous) of deep-reaching erosion after the faulting took place, 

 facilitates our exploration by reducing the constructional form nearly 

 to a baselevel plain, still perceptible in the hard crystalline plateau east 

 and west of the Triassic area ; but the task would be still easier if this 

 great erosion had not been followed by a period of uplift and consequent 

 denudation (post-crctaceous) , in which the softer beds have wasted down 

 ■well towards a lower baselevel surface where they are now generally 

 drift covered, leaving only the crest lines of the thickest and hardest 

 trap sheets to bear witness to the existence of the previous baselevel of 

 the region. When a ridge formed by the main sheet is cut by a fault, 

 the crest of the ridge gradually descends as it approaches the fault, 

 and the two lines intersect on low ground. The crest line curves gently 

 at the northern side of a block, and sharply at the southern, as in Fig. 9; 

 hence the strong bluffs at the south end of the ridges in the neighbor- 

 hood of Meriden. On first recognizing the existence of faults here, the 

 observer may be disposed to postulate a horizontal motion along the 

 fault line, in order to account for the offset of the corresponding ridges ; 

 but there is no necessity of this ; a vertical uplift followed by a base 

 levelling will serve as well, as has been indicated in the diagrams above. 



