1868.] 



MACKINTOSH BRISTOL CHANNEL. 



279 



and states that, among the former, the apparent lines of lamination 

 and stratification are often as distinctly marked as in the latter. 

 His object, however, is not to defend a theory, or to deny that 

 certain granites may be of directly igneous origin and intrusive, 

 but to bring into notice several phenomena in which the linear 

 structure of granite seems to suggest the idea of original aqueous 

 deposition : — (1) a semidetached portion of one of the ranges of cliffs 

 called Hountor Rocks, in which there is the appearance of strata 

 embracing laminae, the second stratum obliquely denuded, a third 

 thrown down on an inclined plane, and horizontal deposition resumed 

 in the fourth or uppermost stratum ; (2) the Kestor Kock, near 

 Chagford, the apparent lamination of which is, in several places, 

 obliquely crossed by fractures of the nature of joints ; (3) the 

 Blackenstone Rock, which presents a very regular series of beds ; 

 (4) the Hey Tors, especially the western boss of rock, in which two 

 very different kinds of granite are separated by a distinct lino 

 parallel to the lines of apparent lamination and stratification below 

 and above. 



4. On the Mode and Extent of Encroachment of the Sea on some 

 parts of the Shores of the Bristol Channel. By D. Mackintosh, 

 Esq., F.G.S. 



Contents. 



1. Introduction. 



2. Form of Sea-coast near Watchet. 



3. Extent of Strata removed. 



4. Recent rate of Encroachment. 



5. Raised Sea-bed. 



6. Encroachments near Weston-super- 

 Mare. 



7. Posttertiary Submergences. 



1. Introduction. — In a paper read before this Society, Nov. 8th, 

 1865*, Mr. Godwin- Austen brought forward very satisfactory 

 reasons for concluding that the area of the Bristol Channel was dry 

 land during the (now submarine-) forest era, and that it must after- 

 wards have subsided to a depth of at least 120 feet, as a submerged 



Eig. 1.' 



land-surface is now found at that depth under the sea-level. 

 Whatever relative changes in level the land and sea may have sub- 

 sequently undergone, it is obvious that the general tendency of the 

 waves and " ground-sea " or " Atlantic drift " (which is sensibly felt 

 beyond Watchet) has been to destroy the contour of the gradually 

 rising shores by wearing them back into cliffs. As a consequence, 

 the extent of the encroachment, since the forest- area went down, 

 may, in some localities, be approximately ascertained. 



2. Form of Sea-coast near Watchet. — Let Fig. 1 represent a trans- 



* See Quart. Journ. Geol. See. vol. xxii. p. 1. 

 VOL. XXIV. — part I. X 



