GEOLOGY 



the rocks as to interfere with the continuity of individual seams as in 

 this quartzite, the same causes have in other cases produced quite an 

 opposite effect ; for instance, the quartzite at Carne, which on the coast 

 of Gerrans Bay below is only a few feet thick, has been so intensely 

 folded that it occupies a considerable area on the hillside above, and 

 presents the appearance of a bed of considerable thickness. In this case 

 the quartzite has been folded, and the folds so packed together that a 

 narrow bed has been made to occupy a considerable outcrop, while on the 

 other hand the quartzite south of Nare Point (St. Keverne) has been so 

 squeezed and dislocated that it is only represented by a series of lenticles. 

 A small quartzite band that occurs in the Falmouth estuary presents 

 similar features. On the coast between Restronguet Point and Porth- 

 gwidden this quartzite seam i or 2 feet thick is represented by a series of 

 lenticles among the folded and brecciated slates in which it occurs. 



The belt of country which is bounded by the coast line extending 

 from Gerrans Bay to the Helford river includes so many estuaries, which 

 penetrate far into the heart of the county, that the tortuous and ex- 

 tensive coast line presents every facility for studying the rock structures. 

 As this area includes several sedimentary divisions and every variety of 

 deformation, a summary of its structural characteristics will convey a 

 very fair idea of the processes of rock-building to which the Palaeozoic 

 deposits of Cornwall have been subjected, as the result of their sojourn in 

 the subterranean depths of the earth's crust. 



A detailed study of those coast sections reveals a complex set of 

 structures, which have been brought about by powerful earth stresses. 

 Folds may be detected immediately in any of the sedimentary divisions, 

 but as the folds are generally isoclinal (closely packed) the plication is 

 not so conspicuous as in a region of normal folding. But the evidence 

 of plication is everywhere so marked that the apparent dip of the strata 

 can only be interpreted as the inclination of limbs of folds. The folding 

 has been accompanied by faults which are almost as numerous as the 

 folds to which they bear a direct relation. 



The faults often occur every few yards, both parallel to the strike 

 (or trend of the beds) and in oblique directions, with the result that the 

 whole rock-mass when seen in ground plan presents the appearance of a 

 huge mosaic. On that part of the coast with which we are now dealing 

 neither large faults nor large folds are common. It would appear that 

 at an early stage of the folding process the resistance to the strains was 

 so feeble that fractures were readily produced. In many districts reversed 

 faults are as numerous as those of normal type. 



Although the rocks are everywhere cleaved we can in most cases on 

 the south coast distinguish between the cleavage and bedding. The 

 alternations from argillaceous to arenaceous material are so numerous that 

 there is little difficulty in distinguishing these structures. The cleavage 

 which is usually oblique to the bedding varies with the nature of the 



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