70 BULLETIN OF THE 
clinal series. A little preparatory consideration of the areal 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 bound 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 therefore 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 observer. This principle is all-important in 
deciphering the topography and structure of the region. Reference 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-cretaceous), 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. 
