Physical Structure and older stratified Deposits of Devonshire. 679 



rous open joints, which in the coarser contorted beds are very irregular in their directions. But 

 when the beds have a finer flaggy or shaly structure, the joints often become parallel, (espe- 

 cially in a direction nearly transverse to the strike) so as to separate the strata into prismatic 



The descriptionabove given oftheculm-measures, is copied from memoranda 

 made on the spot during our traverses through the formation. The prevailing- 

 characters of the formation are the same throughout, and with very few excep- 

 tions (which occur chiefly in the metamorphic portions), there is no difficulty in 

 identifying it by its mineral characters alone. Its dark colour, the imperfect 

 induration of the shale beds, the absence of slaty cleavage*, the coarse me- 

 chanical nature of the bands of sandstone, and the perpetually recurring con- 

 tortions, enabled us to follow it throughout, to trace it round the N.E. flank 

 of Dartmoor, and to make out the boundaries of certain outliers of it which 

 occur near Newton Bushel. And when we combine with these characters the 

 very frequent occurrence of vegetable fossils, we can seldom fail to make out 

 the place and limits of the deposit among the older rocks of Devonshire. 



There are other appearances in the very external aspect of the county to 

 help us in determining the superficial extent of the culm series. The conti- 

 nued undulations of the whole region, where the contorted strata are expanded 

 in a numberless succession of ridges, prolonged east and west like the anti- 

 clinal and synclinal lines of the inferior strata — the great extent of a yellow, 

 sterile, and, we believe, pyritous clay, producing a cold, fruitless soil, exactly 

 like that among the cold lands of our coal-measures |; — these characters often 

 enable us, at a glance, to separate this formation from ah the other deposits 

 of the country. 



Such are the prevailing characters of the two groups into which we have 

 divided the culmiferous series ; and such are the prevailing characters of the 

 subordinate parts : and whatever may be their place in the general scale of 

 British formations, this at least is certain, — that they are more recent than any 

 of the other deposits, described in our transverse section, from the north to 

 the south coast of Devon, and that they are overlaid by no rocks older than the 



thin impure beds of limestone are found in several other places in the upper culm-measures. We 

 are indebted to Mr. Austen for the following localities ; viz. Chittlehampton, Romansleigh, King's 

 Nympton and Bishop's Nympton, High Bickington, Horridge Moor, Instow, and Harwood. 



* We have already described some exceptions to this rule in the shales of the lower group, east 

 of Launceston ; and similar exceptions occur in the metamorphic portions near Oakhampton. 



f The sulphate of iron in the pyritous clays, where it meets with the roots of the oak, sometimes 

 produces streams of natural ink, which discolour the deep cuttings of the soil, by the sides of the 

 cross roads, to a considerable distance. 



