Geology of the South-east of Devonshire. 453 



water over that particular spot. The moUusca so abundant there, are altogether wanting in the Haldon 

 beds, which contain conchifera of littoral habits, mostly broken and water-worn. Nor, in a very large 

 collection have I a single specimen with the valves united, and very few even perfect. 



The greensand beds of the Bovey valley, owing to their covered condition, have as yet afforded fossils 

 from only a few localities, indicated in the foregoing table, and the species are few in number. The 

 Orbitolites, which occur sparingly on Haldon, are exceedingly numerous in beds below Lindridge Hill, 

 forming by themselves layers of some thickness ; the same beds contain Orbiculae. 



§ 3. The New Red Sandstone. — This formation presents, in a direction from east 

 to west (see map, PI. XLL), the following obvious divisions : — 



1st, Marls, containing gypsum in the lines of deposition ; and extending as far 

 as Sidmouth. 



2ndly, Sandstones, as between Sidmouth and Dawlish. 



3rdly, Shingle and conglomerate. 



It is almost unnecessary to observe, that these divisions are not separated by any 

 distinct lines, but that they gradually pass into each other. In general the con- 

 glomerate increases in coarseness towards the western edge of the deposit. 



This formation has been so fully described in the " Outlines of the Geology of 

 England and Wales," Chapter IV., that a few observations as to the mode of its 

 accumulation is all that it seems to require here. 



The rocks which supplied materials for the formation of the conglomerate, are mostly such as are found 

 in the immediate district, consisting of slate, limestone, porphyry, carbonaceous grit, greenstone-trap, 

 and altered shales. Some of the blocks are much water-worn, as the limestones generally towards the 

 edge of the deposit; but taken within its area, as in the cliffs of Teignmouth, they ai'e subangular. 

 It will be found too, that along the boundary-line the conglomerate partakes of the nature of the 

 rocks in the immediate vicinity; as for instance, limestone blocks predominate in the beds facing 

 Marychurch, Barton, Kingskerswell, &c., a circumstance in strict accordance with what was noticed 

 respecting the present sea-beach. In some more central places, on the other hand, the body of 

 water which distributed these conglomerates appears to have set in a constant direction ; for the blocks 

 of porphyry, which, from similarity of character, must have been derived from one source, have a linear 

 arrangement, as may be seen along the Haldons, especially up the Combe Valley ; and, tracing this line 

 down to the sea, we find them occupying the whole vertical thickness of a lofty cliff east of Teignmouth. 

 From the inspection of a very large collection of specimens, I feel confident that these blocks have been 

 derived from the great sheet of porphyritic matter, of which portions still remain, in situ, at the north extre- 

 mity of Great Haldon and other places ; so that we are moreover informed as to the direction in which the 

 materials moved, and the prevailing set of the water which transported them, just in the same manner as we 

 now find oolitic rocks travelling eastward, and mixing with the chalk-flint shingle of the coast of Sussex, 

 but know, that we never meet with a single fragment of that series mixed with the older materials on the 

 beaches or bed of the sea to the west. If the conjecture be correct as to the source from which the 

 porphyritic blocks were derived, from the known fact that they occur in particular places throughout the 

 entire thickness of the deposit, as in the cliff already noticed, we arrive at another unavoidable inference, 

 — that some portion of the porphyritic mass was not covered up, but was so situated as to be exposed to 

 constant destruction throughout the red sandstone period ; whilst it will be seen, in the notice of this 



VOL. VI. — SECOND SERIES. 3 N 



