346 G. WAREING ORMEROD ON THE MURCHISONITE 



21. On the Murcrtsonite Beds of the Estuary of the Ex, and an 

 attempt to classify the Beds of the Trias thereby. By G. Ware- 

 ing Ormerod, Esq., M.A., F.G.S. (Read February 24, 1875.) 



In a paper by myself " On the Waterstone Beds of the Keuper in 

 Somerset and Devon " * a sketch was given of the chief geological 

 features of the coast from Culverhole Point to Littleham Bay, to 

 the west of the Budleigh-Salterton pebble-beds. Since wri ting- 

 that paper I have found pseudomorphous crystals of salt a short 

 distance to the west of Sidmouth, at Windygate, but have not found 

 them to the west of Littleham Bay. The following pages contain 

 an outline of the geology between that Bay and Maidencombe, or 

 Minnicombe, near Torquay. 



The chief characteristic features are the beds in which Murchi- 

 sonite occurs in the higher part, and the conglomerate beds with 

 limestone in the lower part of the series. The last-named beds are 

 specially noticed in Conybeare and Phillips's ' Outlines of the Geology 

 of England and Wales ' (page 293). It is there stated that the 

 fragments in the breccia between Dawlish and Teignmouth consist 

 of granitic and porphyritic rocks in many varieties, grey wacke, or 

 compact sandstone, and Lydian stone, and calcareous rocks with 

 and without organic remains. These fragments, it is stated, may be 

 regarded as being derived from the adjacent rocks at Babbicombe, 

 Chudleigh, Ashburton, and Dartmoor. In the list of granitic and 

 porphyritic fragments those of felspar are mentioned, and these 

 both in the rocks of which felspar is a component part, and in 

 detached crystals ; these for the most part are the opalescent crystals 

 known as Murchisonite. Murchisonite possesses a third cleavage in 

 addition to the two at right angles to each other of orthoclase ; and 

 it is upon this third cleavage -plane that the opalescent play of 

 light is observable. Murchisonite, as found at Dawlish, according to 

 the analysis of Mr. R. Phillips, as given in Greg and Lettsom's 

 Mineralogy (page 107) consists of 68*6 silica, 16*6 alumina, and 

 14-8 potash. 



At " Straight point," the headland to the west of Littleham Bay, 

 there is a bed of conglomerate about 8 feet in thickness, composed 

 chiefly of angular fragments of Lydian stone and porphyry, and 

 about 6 feet below that a bed containing white crystals. The cliffs 

 between that point and the target of the Exmouth rifle-range con- 

 sist of beds of soft red rock, with occasional blue and red clayey 

 beds interstratified, varying greatly in thickness and dipping from 

 about 4° to 5° in the E.N.E. direction. At the point of the high land 

 of Orcombe there is a " throw down " to the east of about 50 feet ; 

 near to the Flagstaff point another fault occurs, which appears to run 

 in nearly a northerly direction; and near the rifle-range target 

 another fault occurs running in the same direction. The cliff at this 

 point is of soft red rock with red clay-bands, and also white clay- 

 * Quart. Journ. Geol. Soc. 1869, vol. xxv. p. 50. 



