A HISTORY OF DEVONSHIRE 



north part of Southdown ClifF, or a local development, is not clear. 

 The dark slates on either side of it contain hard black patches, in one of 

 which on the north side Pteraspis structure was visible. At Scabba- 

 combe Sands the Ringmore beds reappear — dark grey and red shales, 

 and slates with siliceous bands, grits, and crinoidal films, also lenticular 

 red limestone, identical with limestone on East Looe beach (which is 

 characterized by irregular calc spar patches, probably Monticuliporoid 

 corals). The junction of these beds with the Dartmouth slates is in- 

 accessible, and probably a fault. 



Though faults or thrusts have the effect of causing sections in the 

 same rocks to exhibit differences, on the whole the correspondence of 

 the beds on the north with those on the south side of the Dartmouth 

 slates is too complete to be due to accidental similarity in different 

 groups. The Dartmouth slates, so named by Sedgwick, are therefore 

 the oldest Devonian rocks in south Devon and occur in an anticline. 

 Their northern boundary is faulted between Plymouth and Modbury 

 and also near Dartmouth, but near East AUington their persistence is 

 rendered doubtful by the flattening out of the main structure in a series 

 of folds. They consist of slates, shales often silty, with occasional hard 

 grit beds, and exhibit pink, red, green and purple blended tints, but 

 over a large part of their extension their colours are not to be clearly 

 distinguished from those of higher horizons. Their connection with 

 the Pteraspis beds of Polperro has been traced through the intervening 

 area, but their continuity across Cornwall to Watergate Bay where 

 Pteraspis was found in them by Howard Fox is doubtful. Pteraspis has 

 been found at Higher Ford near Wembury, and obscure fish remains 

 in Strete Cliffs. The occurrence of Pteraspis in dark slates on the north 

 of Long Sands and near Ayrmer Cove renders the range of that fossil 

 above the Dartmouth slates very indefinite. The Dartmouth slates are 

 somewhat similar in character to the Gedinnien slates of the Rhine 

 section and to the glossy Gedinnien slates of the Ardennes, and they 

 appear to be homotaxeous with them. 



Under the term Meadfoot beds are embraced rocks corresponding 

 to the Taunus quartzite, etc., rocks of Lower Coblenzien, and possibly 

 in part of Upper Coblenzien age, so unsatisfactory is their boundary with 

 the Staddon grits, which are Upper Coblenzien. The types of the 

 lower beds are taken from the Looe district in east Cornwall, which pre- 

 sents resemblances to all the varieties of rocks in natural or faulted 

 contact with the Dartmouth slates in Devon. The Looe fauna is mainly 

 characterized by such forms as Spirifer primcevus, Orthis bipparionyx^ 

 Rhynchonella pengellyana, Streptorhynchus gigas and Pleurodictyum^ and by 

 irregular calcite patches in the lenticular limestones referred to in all the 

 Devon sections as (?) Monticuliporoid coxz\%. These rocks are cut out by 

 the fault boundary of the Dartmouth slates between Membland and 

 Wembury ; they can in no case be separated from the Meadfoot beds. 

 The tnost fossiliferous rocks, or rather the best preserved fossils, are 

 found in the fault-broken Torquay anticline and in the larger Paignton 



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