644 Professor Sedgwick and R. I. Murchison, Esq., on the 



junks) of nearly pure limestone; and by its numerous, but generally ill- 

 preserved, fossils. Many parts of it so exactly resemble the Caradoc sandstone, 

 that we were, at first sight, led to place it provisionally in that part of the 

 Silurian system. 



Mineral Structure, Thickness, Fossils, Sgc. of the preceding Five Groups. 



In the preceding sketch, we have endeavoured to convey a true notion of 

 the distribution of the natural groups into which the strata of a portion of 

 North Devon may be divided, and of the evidence we have of their order of 

 superposition. We must now add a few words on their structure, fossils, and 

 other characters, by help of which, we may hope eventually to compare them 

 with other rocks of the British series. (See Map, PL L., and Sections I, 2, 

 and 4, PI. LI.) 



1. Our lowest group, as above stated, is seen in the lower part of the Valley of the Lyne, and 

 in the Valley of Rocks, and the cliffs west of Linton. Ascending the valley from Lynmouth, 

 the beds on both sides the river dip nearly north, but at a small angle*. The most striking of 

 them are composed of a hard, close-grained, greenish and reddish siliceous sandstone, much inter- 

 sected by nearly vertical, transverse joints, slightly micaceous, and here and there traversed by 

 earthy, cellular bands, marking the dip, and full of casts of fossils. These harder beds alternate 

 with and pass into soft fissile and chloritic beds, much intersected by planes of cleavage, which 

 hang towards the south — a direction opposite to the true dip of the beds. A little below 

 Waters'-meet, the beds are so much contorted that it is difficult to draw any conclusions from 

 their dip ; and some of them are highly calcareous and fossiliferous. The organic remains are, 



* The same dip is seen in the cliffs on both sides of Lynmouth, and extends a considerable way 

 both to the east and west. Following the base of the cliff towards the Foreland, this northern dip 

 continues about half a mile ; and we reach a point where, in the lower part of the cliff, is a hard, 

 bluish flagstone, with calcareous veins and some obscure fossils ; and in the upper, a hard, reddish 

 gray gritstone, with many quartz veins. We supposed, when on the spot, that these calcareous 

 beds were a prolongation (by the northern dip) of some similar beds seen in ascending the gorge 

 of the East Lyne. Beyond the point of the coast above mentioned, commence some remarkable 

 contortions ; and the dip at the base of the cliff is reversed to the south, for about a quarter of a 

 mile, when a series of magnificent contortions, by which the beds are almost twisted into re-en- 

 tering curves, and enormous masses are almost compressed into ellipsoids, are again seen in the 

 cliffs, where the coast turns and trends more directly towards the north. Beyond this part of the 

 cliff, there is a steady dip to a point about N.N.E., and at a great angle, and it is continued into the 

 reefs at the furthest point of the Foreland. Considering the enormous thickness of the coarse red 

 grits which extend into the Foreland, we do not see how they can be correctly packed under the 

 Linton calcareous group, consistently with the dips above indicated. Our interpretation probably 

 requires a downcast fault to the north, cutting through the contorted beds. Mr. De la Beche's 

 explanation seems, on the contrary, to require an upcast fault to the north. In a previous note 

 (p. 642) we have endeavoured to show that our explanation harmonizes with the general structure 

 of the district. 



