388 PROF. J. l'\ BL\KE ON 'IllE MONJAN AND 



constitute the sum total of our available knowledge of the Long- 

 mynd group of rocks. It will be observed that thej- present us with 

 two views, partly discordant and partly concordant. According to 

 Murchison, Salter, and the Survey, these rocks form the base of a con- 

 tinuous series, and are of Cambrian age. According to Dr. Calla- 

 way they are isolated by faults from every succeeding rock (below 

 the Ordovician), and, if of Precambrian age, are at least younger than 

 the Uriconian, of which they contain fragments. Both view^s agree 

 in considering them as a single series, and in denying that there is 

 amongst them anything older than both Cambrian and Uriconiau. 



Now the totally unexpected result of my examination is to show 

 that within the Longmynd area there are two unconformable groups, 

 one of which is older than the Uriconian, and the other of basal 

 Cambrian age. I must admit at once that this result is by no means 

 immediately obvious, and that there are many difficulties to be over- 

 come, principally arising, I think, from the way in which the rocks 

 have been squeezed together ; but while the many points which 

 make against this view can all be explained away, those which make 

 for it can in no wise be accounted for in any other way that is in 

 the least degree acceptable. To a very large extent the whole question 

 is one of detailed stratigraphy. 



§ II. SxiiATIGKAPHY OF THE LoNGMYND HiLLS. 



I. General. — It has been noted above that in describing the Long- 

 mynd rocks Murchison and Salter made respectively six and eight 

 subdivisions of the rocks below the red grits, which form the 

 upper part of the series. In taking a single section, such as that 

 of Carding-Mill Glen, or the Ashes Hollow, we might, if we 

 pleased, make twenty or thirty subdivisions. The whole series 

 consists of well-stratified rocks in conformable succession, made 

 up of various-coloured slates and grits, and greywackes of various 

 hardness and coarseness. But I have not found it possible to trace 

 acro=!s the country more than five groups, and even with these it 

 would in many cases be impossible to say of an isolated exposure to 

 Avhich group it should belong. In all of them there are bands of 

 hard grit, which may occur anywhere, in most there are small masses 

 of purple-looking slate, which, if more abundant, would indicate per- 

 haps another group (see figs. 1, 2, 3). 



The five groups I have adopted are as follows : — On the 

 eastern side we have (1) a series of dark thin shales, which 

 are usually very soft, and contain bands of calcareous matter, corre- 

 sponding apparently to Nos. I & 2 of Salter. To the west of these 

 succeed (2) a series of more solid rocks, many of them hard grey- 

 wackes, but many pale-coloured slates. When these are seen well 

 preserved, as in Minton Batch, they show a beautiful banding, being 

 composed of innumerable small beds, 2 or 3 inches in thickness, 

 with a fine ripple-drift lamination ; but very often they seem so 

 compacted together that bedding is difficult to perceive at all. These 

 I call the "■ banded series." Further west comes (3) a mass of purple 



