Vol. 51.] ' CRUSH-CONGLOMERATES ' OE THE ISLE OP MAN. 593 



shown by the distortion of the planes of shear-cleavage where 

 the matrix has been much nipped between two adjacent fragments. 

 (See PI. XX. fig. 1.) 



When, however, an attempt is made to assign each structure in 

 the rock to the earlier or the later movements very great difficulties 

 crop up, chiefly owing to the tendency there would be for the shear- 

 cleavage to follow the lines of weakness initiated by the first crush- 

 ing of the rock. 



That the 'conglomerate' is cataclastic and not epiclastic might 

 have been, I think, predicted from the examination of the slide and 

 specimen. In the first place, the nature of the conglomerate, slate- 

 and grit-particles in a slaty matrix is. to say the least of it, a very 

 unusual one ; it is difficult to see how such a conglomerate could 

 result by a deposit from water. In the next place, the absence of 

 extraneous fragments is most suggestive, all the fragments being 

 such as are found bedded in the Skiddaw Slate Series of the Island. 

 Further, the examination of the shape of the fragments leads to the 

 same conclusion. Working along the slide from right to left one 

 seems to be following a bed of grit ; first it is slightly bent, next it 

 is more sharply folded and almost faulted, then nearly pinched off by 

 a sharp wrench, and at last it is actually torn off, and one realizes 

 that one has been tracing a fragment and not a band, or, rather, 

 that one is watching the actual method of forming a fragment or 

 fragments out of a band. This phenomenon is illustrated by 

 PI. XX. figs. 2 & 3. It may be seen again and again, and in places 

 smaller bits of such fragments will be seen wrenched off and still 

 standing in close proximity to their parent masses. 



Few of the fragments in the slides studied are entirely rounded ; 

 usually one or two corners are rounded off, while the rest are sharp 

 and angular. When this is the case there is sometimes evidence 

 that the round end of the fragment has moved forward (sheared) 

 through the matrix, distorting the cleavage-planes as it did so. In 

 fig. 4 of PI. XX. the fragment seems to have moved through the 

 matrix and distorted the ' shear-cleavage,' so that it reminds one of 

 the waves running off the bows of a moving steamer, or the waves 

 in Prof. Boys's bullet-photographs. 



A peculiar feature is that some fragments are rounded and 

 ' pebbly ' at one end, while at the other they have behaved as 

 matrix and have had other ' pebbles ' jammed into them. This is 

 illustrated by figs. 1 & 3, PI. XX. In this case the reason is 

 obvious : the ' pebbly ' end is coarse-grained and resisting, the 

 'matrix' end is made of finer, softer material. 



Without going into further minute detail, the appearance of the 

 slide may be thus summed up : — Fragments are bent, twisted, 

 broken, faulted, and floated off from one another ; one fragment 

 indents another, or has another bent or broken over it ; wisps and 

 shreds of matrix are caught up amongst adjacent fragments — torn, 

 faulted, and teased out, or rounded and made into ' pebbles ' where 

 there is more space for them to move ; the matrix and fragments 

 are in places so inextricably mixed up that it becomes impossible 



