BASAL CAMBKIAN ROCKS OF SHROPSHIRE. 401 



boundary has to be drawn as a zigzag-lino. This is best seen near 

 Norbury and Cothercott on the western boundary, and near Church 

 Pulverbatch on the eastern, and many sections show intermingling 

 of the two kinds of rock. The phenomena are thus quite distinct 

 from those of the unconformable junction, and I judge they are 

 entirely due to an intercalation of deposit which thickens rapidly 

 towards the south, and dies out towards the north. It is obvious 

 that if there were here a synclinal and it actually died out, we 

 ought to be getting to its base, in which case the isoclinal expla- 

 nation fails, in face of the still nearly vertical position of the alter- 

 nating strata. 



The western purple grit, which constitutes the third member of 

 the upper series, is very similar to the eastern, and, like it, contains 

 sporadic bands of conglomerate. As every available exposure has 

 been examined, I am prepared to say that the extent of its con- 

 glomerates cannot well be much greater than is marked on the 

 map, which indicates that they are less continuous and narrower 

 than in the other, and occur on several distinct horizons. I have 

 sought in this conglomerate also for fragments other than of quartz, 

 but they are far more rare, only three specimens in all the expo- 

 sures having tempted collection. These are all quartz-felsites, one 

 of them very spherulitic. The contents are therefore not so various 

 as in the lower bed ; and the upper one may be properly termed a 

 quartz-conglomerate. In the grit itself there are more signs of 

 bedding, and in most places the dip is still high towards the west. 

 However, at the northern end, in the neighbourhood of Pontesford 

 Hill, we find the only examples of reversal of dip in the whole area. 

 Thus in the great crag of conglomerate in Oaks Hill, though the beds 

 are nearly vertical, they do incline towards the cast ; and in the 

 river-section above Lyd's Hole there is an undoubted easterly dip 

 of about G0°. It is very tempting to consider these to be the true 

 dips as Dr. Callaway has done, and to infer that the rocks which 

 succeed them to the west are of an underlying series. Eut M'e are 

 here in the presence of a large mass of igneous rock, which at least 

 may be intrusive, and therefore we should be cautious, and take our 

 observations, as far as may be, away from such possible disturbers. 

 Leaving, then, this Lyd's Hole district for the moment, we will go to 

 the extreme south, — to the other end of the range. Xow here we 

 may observe numerous dips throughout the whole extent of Liiiloy 

 Hill, and they are always rather low and to the west, no dip being 

 above ()0°, and one as low as 20^ It is in this district also that we 

 meet with other rocks which, from their intercalation with the purple 

 grit, seem to follow it in regular sequence. This, I take it, supplies 

 us with the true reading, and proves that there is no syncHnal. 



It may seem remarkable that the ])cds of the upper series, if it be 

 unconformable to the lower, should nevertheless have the same ap- 

 proximate strike. But this is easily accounted for. Where the grits 

 and conglomerates mount on to the summit of the Longmynds, tliey 

 do not possess the same strike ; but when developed in the already 

 denuded valley to west, the subsequent pressure has pushed them up 



