305 



others in whicli they are abundant; the bands with many 

 pebbles are, however, unstratiiied. Above this is 20 to 30 feet 

 of sandstone, with small pebbles, and, at the summit of the 

 section, a second coarse conglomerate, the pebbles in which, 

 however, do not attain the dimensions of those in the lower 



coarse accumulation The pebbles consist of fragments 



of grits, argillaceous strata, and volcanic rocks .... They 

 possess the outward form of glacial boulders, but a number 

 of them, especially of the fine argillaceous rocks, show 

 unmistakable signs of being slickensided, though a few 

 scratches are found here and there which it would be difficult, 

 if not impossible, to distinguish from glacial striae." The 

 resemblance to glacial features was still further present in 

 that, at one spot, ''the rock beneath (a coarse red sandstone 

 with small scattered pebbles) was found to be marked by 

 ^roovings.. There are two principal sets of these, crossing 

 each other at an angle of about 40°." 



In 1898 J. B. Hill, of the British Geological Survey, 

 described a zone of brecciation in the Mylor (Devonian) series, 

 at Gerran Bay, Cornwall. The features were included in 

 ■''finely-striped slates" and were, at first, regarded as original 

 clastic deposits. The brecciation extended for half a mile 

 across the strike, "the strata being made up of a mass of 

 fragments from the size of peas up to 5 or 6 inches in length, 

 enveloped in a slaty matrix." The fractured rock is 

 'associated with faulting in the last stage of folding." (ii> 



Mr. Hill, in 1901, published an article "On the Crush- 

 conglomerates of Argyllshire." (12' These occur in the 

 Dalradian schists and were, in the first instance, regarded as 

 clastic sediments. The beds have been subjected to isoclinal 

 folding, which has, "in some instances, proceeded so far that 

 the rock-sequence is now represented by a banded zone in 

 which the alternations are so narrow that they range from 

 a foot to as little as an inch in thickness. While in some 

 cases the process has ended here, in others it has been carried 

 a stage further, and the closely-packed folded bands have 

 been divided by shear-planes severing the continuity of the 

 limbs until lenticular fragments have been produced more or 

 less isolated, culminating, by the rolling out of the lenticles, 

 in the production of pseudo- or crush-conglomerates." The 

 crush-conglomerates occur most commonly near the junction 

 of rocks of dissimilar character, especiairy so in the junction 

 of epidiorite and limestone. The limestone is coarsely gritty 



(11) Hill, Memoirs Geolog. Survey United King., Summary of 

 Progress, 1898, pp. 92, 93. 



(i2)Qiiar. Jour. Geolog. Soc, vol. Ivii., 1901, pp. 313-327. 



