Geology of the South-east of Devonshire. 



481 



so that the agreement is only occasional. Throughout South Devon the planes which have a southern 

 dip, and consequently a direction about east and west, are always the smoothest and best ; on the 

 Newton and Totness road, at Little Hempston, Staverton, north-west of Totness, &c., two planes or 

 more may be observed, whilst in the slates N.E. of Plymouth there are as many as four systems of planes, 

 all distinct from that of deposition. 



This structure is not confined to the slate rocks, the cleavage planes passing equally through the sub- 

 ordinate bands of the contemporaneous hornblendic beds, as at East Ogwell (PI. XLII. fig. 3)and Datton 

 Mill; and affecting also masses of limestone of vast thickness, as about Gatcombe, two miles N.E. of 

 Totness, and Bunker's Hill, where it is often diflScult to ascertain the bedding in consequence of the more 

 strongly marked lines of cleavage. 



Many facts illustrative of the jointed and cleavage structures may be collected in that part of Torbay 

 where the slate rocks come down to the coast between the limestone and new red sandstone. 



The great limestone masses about Brixham have similar cleavage planes, cutting through their entire 

 thickness with striking regularity (fig. 17.) ; the bedding here being also very distinct. This structure is 

 not confined to the old rocks of South Devon, nor is it any proof of their priority, as they do not alone 

 afford roofing-slates. Throughout the carbonaceous series, slate-quarries are very numerous, but in no 

 instance that I know of, are they worked parallel with the bedding. In a large quarry near Lew Trench- 

 ard, roofing-slates alternate with coarse flagstones (fig. 18.); the latter subdividing parallel with the 



Fig. 17. 



Fig. 18. 



Oblique cleavage planes in roofing-slate (a), and horizontal 

 ■' ' in coarse flagstone (4) near Lew Trenchard. 



Cleavage in limestone near Brixham. 



planes of deposition, but the intermediate slates cleaving at a high angle. The contortions of this 



series of deposits are so constant and extraordinary, that illustrations of every possible position of the 



Fig. 19. 



Cleavage planes in arched strata near Yealm Bridge. 



plane of cleavage, with relation to strike and dip, may be found often in a single quarry. The wood- 

 cut (fig. 19.) represents a section across the large slate-quarry near Yealm Bridge, at the back of Wer- 

 rington Park, worked in arched beds of the carbonaceous series, and where the cleavage planes obviously 

 conform to the lines of deposition at one place, and at another, within a very short distance, cut them 

 at right angles. The older series of deposits which rise from beneath the carbonaceous beds on the 

 north, if followed along the coast-section, exhibits the very striking fact of cleavage planes, w'th one 

 constant angle and direction, cutting through strata of various mineralogical characters and most curi- 



