BASAL CAMBEIAK ROCKS OF SIIKOPSHIKK. 389 



slate of very schistose character, but soft. There are some bands of 

 grit, but; on the whole it is very free from them. This is Xo. 4 

 and part of 5 in Salter's list. Pollowing on we find (4) a large quantity 

 of hard and often micaceous greywacke, seen in Carding-Mill Glen 

 to contain many intermediate bands of slate, but the greywacke, 

 being in greatest abundance, almost always forms the isolated ex- 

 posures. This is Salter's I^o. 0. Lastly we find (5) a pale greenish 

 slate which weathers purple, and is easily taken for Xo. 3 till a 

 fresh fracture is obtained. Associated with this are bands of purple 

 grit and greywacke, often micaceous. There is so intimate a mix- 

 ture in some places of these two kinds of rock, and such a segrega- 

 tion in one place of slates and in another of greywackes, that I 

 cannot separate them into two. They correspond to Nos. 7 and S 

 of Salter, and 5 and of Murchison, whose descriptions of them, no 

 doubt taken in different glens, do not coincide in details, because 

 they both are true of particular sections. 



Practically the above description is the same as Murchison's, with 

 the exception of the last item. 



The subdivisions in the lower part of the Longmynd rocks, which 

 I have here enumerated, are given in geographical succession, because 

 it may be doubtful which is their order of succession in time. This, 

 however, is the first point to settle. Murchison and every one else 

 reckons No. 1 the lowest, and I think it is so, but it requires defi- 

 nite proof. In the first place there is a pretty uniform dip towards 

 the west, only locally disturbed, and then so very irregular as to be 

 obviously accidental. Thus if the rocks do not succeed in time as 

 wo pass west, they must be throughout inverted. Again, there are 

 numerous surface-markings in some of the groups, especially in the 

 purple and pale slates, the best known of these are the little hollows 

 referred to the borings of Annelids. Now wherever these are seen 

 it is the hollows that face west and the elevations which fit into 

 them that face east. If they were really Annelid-burrows, it would 

 prove the point, but this is by no means certain. However, the 

 specimen in the Museum of Practical Geology collected by Mr. 

 Salter, and figured by him in his second paper (Q. J. G. S. vol. xiii. 

 ])1. V. fig. 1), supplies the required evidence. On this there 

 are at the same time ripple-marks, rain-spots, and the minute 

 depressions. Now of rain-spots we can be in no doubt, the con- 

 cavity must be on the upper side, and in the specimens the 

 depressions are on the same side as the rain-spot concavities. Hence 

 the upper side of the rock faces west. A third reason for believing 

 this arises from the nature of the rocks. Those on the east are en- 

 tirely unlike the overlying purple grits ; but the group which lies 

 most westerly is so like the succeeding beds, as to give rise to great 

 difficulties, and suggest in some places almost a passage between the 

 two. It is far more probable that this is a true appearance than 

 that the basal beds of two groups should be so much alike : and if it 

 should be accepted that the overlying grits are unconformable to 

 the whole of the series, we may expect the included fragments at 

 the base to have been derived from the uppermost rocks. Now 



Q. J. G. S. No. 183. 2 f 



