Vol. 55-] 



THE GRAVEN DISTETCT OF YORKSHIRE. 



345 



its base is a thick band having a mottled appearance where un- 

 weathered, but the weathered part shows that it is a veritable 

 breccia. In section, it shows the suture-like edges of the fragments, 

 and the schistose structure of the matrix which has been noted in 

 the case of the Draughton breccias. A little above this is a foot or 

 more of grey pasty rock resembling shale in appearance, but pro- 

 bably crushed limestone, with angular and even rounded fragments 

 forming a true crush- conglomerate. Much horizontal slickensiding 

 is seen through this breccia, as well as along the bedding-planes of 

 limestones in various parts of the quarrv. 



The breccias formed of irregular lumps of limestone occurring in 

 shale seem to 



Fig. 10. — Limestone, broken along joints, with de- 

 tached fragments on the right hand, Otterhurn 

 VaUey. 



Fig. 11. — Folded limestone and hrecciated fragments, 

 Otterhvrn Valley. 



me to have 

 been also 

 produced in 

 two ways. 

 In the first 

 place, bands 

 of limestone 

 may become 

 torn apart, 

 and form iso- 

 lated patches. 

 Fig. 10 shows 

 a band of 

 limestone 

 near Pot- 

 house, Long 

 Preston, 

 w^hich is 

 cracked 

 across along 

 joints, and the 



fragments are slightly separated on the left side, the interstices being 

 filled with veins of calcite, while on the right actual separation has 

 occurred, and the shales sweep in between the fragments. Breccias 

 of this nature would naturally be formed where thin limestones 

 with shales were stretched, as the limestones would resist stretching 

 more than the shales, which yield frequently along the lamination- 

 planes, and also have their particles flattened out. In this case the 

 teazing-out of fossils may be frequently observed on the surfaces of 

 the shales. In other cases passages are observed from thin lime- 

 stones, in shales which have been folded and faulted, into detached 

 fragments of limestone, the resulting breccias being produced by 

 stretching along portions of rock which have been locally compressed. 

 Fig. 11 shows a detached fragment of limestone close to the end 

 of the bed from which it has been torn, with a loop due to 

 folding, and smaller fragments above. In fig. 12^ (p. 346) a breccia 



^ This figure is reproduced from a photograph taken by E. J. G-arwood, M.A., 

 F.Q-.S. A fault runs obliquely down from near the centre towards the left-hand 



