Vol. 55.] 



TSE CRAVEN DISTRICT OF YORKSHIRE. 



335 



bent, so that the rock appears to have suffered compression and 

 subsequent stretching. Under the microscope, a section of this 

 rock shows that the rod-like masses are separated by very fine 

 joints. The rock has been subjected to pressure to so great an extent 

 that it exhibits a structure closely resembling flow-structure : in fact, 

 it has the mechanical characters of a schist. The fragments of 

 organisms are arranged with their longer axes 

 parallel to the ribboned lines which have been 

 ' developed, and often stream around larger frag- 

 ments. The lenticular patches appear to consist 

 of portions of the rock which have been more 

 completely rolled out than those portions by which 

 they are surrounded. 



The remainder of the bauds to be described are 

 below the breccia. In the centre of the middle 

 shale is a thin calcareous band, seldom more than 

 r 1 inch thick and usually much less, which is of 

 Iq great interest. It is largely composed of crinoid- 

 \ joints, and when at its thickest these are easily 

 j apparent. It is traversed by wavy lines parallel 

 ! with its top and base, and suggestive of flow- 

 ; structurerather than lamination. When the band 

 \ is thinner, the fossils are less apparent, while the 

 I divisional planes come closer together and more 

 I nearly approach exact parallelism. At its thinnest, 

 ^ the fossils have almost disappeared, and veins also 

 I occur along the divisional planes. Microscopic 

 I sections of the three types have been examined, 

 g \ [ ^ In the first stage the rock is practically a breccia, 

 I fragments of very fossiliferous limestone being 

 ij surrounded by a matrix consisting of the original 

 I rock rolled out into a schistose-looking substance. 

 1^ In the second stage the fragments have been 

 further comminuted, so that only the smallest 

 fossils occur in a state approaching perfect pre- 

 servation ; the matrix has been further dragged 

 out into attenuated lenticles ; and the whole struc- 

 ture has the mechanical characteristics of a fine 

 schist. In the third stage, the slice examined 



A showed little beyond the veins of calcite which had 



been developed along the plication-planes of the 

 rolled-out rock. 



In the limestone below the middle shale is a 

 remarkable chert-band (see fig. 3). It forms a series of lenticles, 

 sometimes in contact, but often isolated. The chert may have been 

 formed in this manner, but its appearance is much more suggestive 

 of stretching. It is much veined. Under the microscope it shows 

 little of interest, except the calcite-veins which have filled up the 

 interstices produced by stretching of the rock. 



The limestone below that containing the chert-band is about 



