398 TROF. J. r, TJLAKE OX THE MONIAX AND 



northern end at Hougbmond Hill, though at Lyth Hill it lies in 

 the middle, and a smaller conglomerate band and a mixed series of 

 grits and slates form the base. In the southern outlier, near Hope- 

 say, there is an almost entire absence of conglomerate ; the only 

 places where I have seen it being the summit and slopes of Wartle 

 Knowl, where it is apparently at the base. Prom these facts I 

 conclude that the conglomerate has no chronological significance, 

 but is a mere accident in the formation of the purple grits, de- 

 pendent on the part of the surrounding country which at different 

 epochs supplied material to diiferent districts. Even where the 

 conglomerate does not occupy the nearest position to the line of 

 junction, and there seems to be a great mass of purple grit between 

 it and the lower series, we cannot assume that this underlies it, 

 since the inliers in the middle of the Longmynd, unless brought up 

 by faults, have nothing between them and the conglomerate. More- 

 over, the absence of bedding prevents our knowing anything of the 

 dip, while the fact of the purple grit overlapping the slates and 

 greywacke's seems to show that it is, on the whole, not far from 

 horizontal. It was therefore laid down subsequently to the primary 

 disturbances which set the slates on end. 



"With regard to the contents of the conglomerate, we have already 

 a valuable account from Dr. Callaway*, who, in association with 

 Prof. Bonney, describes eight examples, together with two specimens 

 from Haughmond Hill, belonging to the lower series, which are not 

 described in the same terms as the others, but are supposed to have 

 been derived from the denudation of mica-schists. Pour others are 

 from the grits, in which it is noted that many fragments are those 

 of volcanic rocks, a conclusion which I can confirm. 



The nature of the conglomerate at Haughmond Hill scarcely re- 

 quires the microscope to demonstrate, the bulk of the pebbles being 

 of purple rhyolite. Dr. Callaway also notices a pale green felsite, 

 and I can add a fine-grained altered ash. But this conglomerate, 

 so obviously derived from the ancient volcanic rocks of the neigh- 

 bouring Wrekin, is exceptional. So also is the conglomerate of 

 Wartle Knowl, which is largely derived from an associated rhyolite. 



The main conglomei'ates of the Longmynd are, on the contrary, 

 principali}' composed of quartzite. The bed which lies to the east, 

 whose range I have been hitherto describing, contains, I shouM 

 think, about 95 per cent, of quartz- and quartzitc-pebblcs. The 

 question is, whence were these pebbles obtained ? There is, to my 

 knowledge, absolutely no quartzite in the volcanic series (the over- 

 lying quartzite is obviously of later date than the conglomerate), 

 nor do granitic rocks readily yield such fragments. Yet, from their 

 abundance, we are certain that there must have been a large mass 

 of quartzite, or quartz-veins, in the neighbouring Pre-Cambrian 

 rocks. The only indication of such rocks that I have met with has 

 been the abundant quartz-veins which render some portions of No. 4 

 and 5 almost a breccia. If the quartz-pebbles were not derived from 



■"' Quart. Jouru. Ck-ol. Soc. vol. xlii. 



