Vol. 6$.~] CARBONIFEROUS ROCKS OF DEVON AND CORNWALL. 7 



folds are rare, while sharp folds predominate. In some cases the 

 anticlines are perfectly regular, and well preserved, though usually 

 faulted through the crest, but with a small downthrow of a few 

 feet or less. 



One of the best-preserved anticlines is that occurring at Tut 

 Hole in Cockington Cliff, rather more than 2 miles south of 

 Westward Ho ! A rough sketch of this fold, which was described 

 as a 'hut-like contortion near Cockington Head, Bideford Bay/ 

 was figured by De la Beche x in 1839. At present the anticline 

 measures 50 feet in height, 70 feet across the base, but it is to 

 some extent crumbling away above. The rocks consist of alterna- 

 tions of sandstones and shales, occurring in an area in which shale- 

 beds for the most part prevail. I am indebted to Mr. Rogers for 

 carefully measuring the dimensions of the fold. 



Other anticlines on an even larger scale, and almost equally 

 regular, if not quite so well-preserved, are to be found along the 

 coast, especially to the south of Hartland Point. McMahon a has 

 well described those occurring near Bude. 



In some parts of the coast-section, sigmoidal and overthrust- 

 folds are extremely conspicuous in the cliffs. The contortions may 

 be so numerous as to be evident in a hand-specimen. Not only 

 can every stage in the formation of these complicated folds be 

 traced, but the rocks concerned show abundant evidence both of 

 crumpling and of compression and crushing. Contorted rocks are 

 especially conspicuous at Dyer's Lookout, near Blackpool Mill, to 

 the north of Hartland Quay, and also at Broadbench Cove, rather 

 more than a mile to the north of Welcombe Mouth, near the border- 

 land of Devon and Cornwall. McMahon 3 has described some of 

 those occurring in the neighbourhood of Bude, and has given a 

 sketch of the contortions at Efford Ditch, to the south of that town. 

 Fig. 1 (p. 8) shows the contorted shales and sandstones exposed 

 in the sea-cliff north of Broadbench Cove. For this photograph I 

 am indebted to Mr. W. H. Friendship, of Bideford. It was taken, 

 with the assistance of Mr. I. Rogers, under great difficulties. 



The rocks in this district may probably be regarded as typical of 

 the Upper Carboniferous Series of Devon and Cornwall. McMahon 

 has studied the petrology of the rocks around Bude, and has given 

 a chemical analysis of one specimen. It may be of interest to 

 recall that he paid special attention to those beds which had under- 

 gone the greatest amount of crumpling, compression, and crushing, 

 to ascertain whether any mineralogical changes had taken place. 

 The conclusion at which he arrived was that they are practically 

 unaltered. He regarded these deposits as derived, not from the 

 weathering of a pre-existing tract of sedimentary rocks, but ' from 

 the waste of a crystalline area,' the materials of which ' appear 

 to have been deposited in tranquil water undisturbed by strong 

 currents.' 4 



1 De la Beche (39) p. 123. - McMahon (90) p. 106. 



3 McMahon (90) p. 106 & text-fig. on p. 107. 4 McMahon (90) pp. 112, 113. 



