592 MR. "W. W. WATTS ON THE [Nov. 1895, 



surfaces of the latter. The slide described is cut at right angles to 

 all three structures. 



Turning to the slide, the fine band is seen to be a grit made up 

 of angular quartz-grains varying from *002 to '001 inch in length. 

 The coarse bands are conglomeratic, and consist of fragments from 

 "100 to "125 inch long, dispersed in a slaty matrix : this frequently 

 contains grit- particles set in a fine-grained, fibrous material, "which 

 appears to be chiefly chlorite. A fine slaty substance of this 

 description makes up the fine dark laminse which separate the 

 conglomerate-bands from the grit and from each other. 



The fragments in the conglomerate-bands are made up chiefly of 

 grit similar to that just described, of still finer grit, and of slaty 

 rock in which mica is rather freely developed. No fragments of 

 igneous rocks, or indeed of any other rock than those just men- 

 tioned, have yet been discovered in the crush-conglomerate. 



Signs of great crushing are at once observable tbroughout the 

 slide ; faulting, contortion, and cleavage are all present, and the 

 quartz-particles in the grit, and especially those in the slate, are 

 nearly all phacoidal in outline. 



Turning next to the divisional planes to be seen in the slide, the 

 following phenomena are important. Taking the main grit-band as 

 a direction of some significance, and without stopping to enquire 

 exactly whether it represents bedding or what not, we find that it 

 bears no relation to other very important structures of the rock. The 

 ' shear-cleavage ' of Lamplugh is well developed throughout the rock, 

 and especially in the finer-grained portion. It is a true contortion- 

 cleavage, and it appears tobe the same as 'aus weichungs-clivage* 

 and the 'strain-slip' cleavage of Bonney. This structure, when 

 best developed in the slaty matrix, is at an angle of about 30° 

 to the general direction of the grit-band ; it runs in the same 

 direction in most of the slate-fragments. It is noteworthy that it 

 is only in such fragments as have their laminae at right angles to 

 the strain-slip direction that the structure is at all characteristically 

 shown ; these alone show contortion clearly. Those otherwise 

 orientated are merely crushed, and do not display so clearly the 

 reason for the cleavage-planes which traverse them. The difference 

 of 30° in the direction of the lineation of the rock and of its 

 cleavage shows that the latter structure is to some extent inde- 

 pendent of the former. 



That the ' shear-cleavage ' has acted on the rock when it was a 

 1 conglomerate ' is evidenced by two facts. When an edge of a frag- 

 ment is at right angles to the shear-cleavage the fragment and the 

 matrix are seen to have been contorted and even faulted together 

 (see PL XX. fig. 4). The shear- cleavage is perfectly developed only 

 in the slaty matrix and slate-fragments, and very imperfectly in 

 the gritty fragments and bands. When, however, there has been 

 exceptional movement and crush, the planes travel into the coarser 

 constituents from the finer (see PI. XX. fig. 3). 



On the other hand, that the movement (a shearing movement) of 

 the fragments through the matrix had not ceased is not improbably 



