504 PKOr. H. A. NICHOLSON AND MR. J. E. MARK ON 



It is noticeable in this connexion that we get several complexes of 

 acid and basic intrusive rock in the North of England, 8iich as 

 might well supply material for the formation of the Ordovician 

 lavas. The rock of Thack Moor is chiefly felsitic, and though it 

 covers a considerable amount of ground, it is usually much decom- 

 posed at the surface. Two other felsitic masses occur to the south 

 of this, one parallel with the Maiden Way and the other beneath 

 Cocklock Scar. 



The only other intrusive rock to which we would call special 

 attention is a broad mica-trap dyke seen in Dry Sike, east of 

 Melmerby, and which is of interest from the greater metamorphism 

 produced along its margin than is usual with this class of rock in 

 the North of England. 



b. The Western Portion of the Inlier, — The rocks on the western 

 si,de of the Knock Pike-Flagdaw Eault consist exclusively of the 

 upper portion of the Ordovician and the lower part of the Silurian 

 rocks, so that along the line of the above-mentioned fault the 

 greater part of the Borrowdale series of rocks appears to have been 

 cut out. The general strike of the rocks is N.W. and S.E., 

 showing a marked divergence from that which characterizes the 

 beds of the more central portions of the Lake District. 



One of the principal features of this half of the Inlier is the 

 existence of a set of N.E. to S.W. faults, which causes frequent 

 repetition of the Upper Ordovician and Lower Silurian rocks. By 

 these faults the west side of the Inlier is divided into a series of 

 rectangular or triangular blocks, with a similar succession in each, 

 and it will save space if we describe in some detail the block which 

 exhibits the most complete section, and afterwards note similarities 

 and discrepancies. 



The rhyolitic pyramidal hill known as Dufton Pike is separated 

 from the similar hill of Knock Pike to the north by one of the 

 above-mentioned transverse faults, which may be spoken of as the 

 Cosca Eault. To the N.E. of this fault, the stream called Swindale 

 Beck runs along the south-east flank of Knock Pike to the village 

 of Knock, and in it the following section is displayed (PI. XYIL). 



The line of the Knock Pike-Elagdaw Eault is here marked by an 

 intrusive mass of mica-trap noticed in Appendix I. The shales on 

 the east side of the fault, the dyke itself, -and the rhy elite are all 

 exposed in a small quarry by the side of the moorland road, N.W, 

 of the beck. Below this a capital exposure of the rhyolite (2) 

 which forms Knock Pike is seen in the course of the stream. It i& 

 succeeded by thin layers of rather fine, apparently unfossiliferous- 

 ashes, which seemingly pass up into the remarkable beds numbered 

 3 in the section. These consist of calcareous shales, with nodular 

 masses of limestone, crowded with fossils, some of the calcareous 

 bands being exclusively composed of the valves of Beyrichia. One 

 bed of the series has been spoken of by Professors Harkness and 

 Nicholson * as the " Discina-corona bed," and we propose to name 



* Quart. Journ. Geol. Soc. vol. xxxiii. (1877) p. 463. 



