BASAL CAMJililAX K0CK8 OF SHKOl'SHIKE. 407 



la Caer Caradoc the unaltered adjacent patch at the south-west 

 is very probably faulted. On the southern slopes is a band which 

 we should call either halletlinta or altered slate, according to the 

 series to which we supposed it to belong; and near the summit is 

 another band ^^'hich can hardly be anything but the latter ; but the 

 most remarkable is in Little Caradoc. Here, crossing the hill be- 

 tween the rhyolite on one side and the dolerite on the other is a 

 very clear band of not much altered slaty greywacke, clearly bedded, 

 and impossible to imagine to be in its natural position. Under the 

 microscope it is seen to be marked with transverse cleavage-lines of 

 sericite, parallel to which the long axes of the quartz fragments have 

 been turned so as to lie across the bedding. From its position and 

 outcrop it is rather difficult to get it here by faulting, but easy to 

 explain as the solid underlying rock on either side of which the 

 igneous extrusions have been made. A very similar band, about 

 which the same may be said, occurs in the Lawley. 



It is a remarkable circumstance that all the localities of these 

 altered slates are connected with the western margin of the range ; 

 and there is nothing like them in the whole of Cardington Hill. 

 The same may be said of the Wrekin area. Nothing that can be 

 thought to be altered slate is found in the Wrekin itself, and the 

 only rock of the kind is at Wrockwardine village, near the >vestern 

 border of the exposure of old rocks. 



The first conclusion, then, at which 1 arrive is, that the volcanic 

 rocks are younger than the slates, and have been extruded from 

 their midst. 



The next point to be considered is the age and character of the 

 masses of coarse crystalline rock, of acid type, called granitoid by 

 Prof. Bonney and Dr. Callaway. The principal mass of this type 

 occurs in the Wrekin, where the former author says of it " there 

 can be no doubt that it is far older than the rhyolite, and thus we 

 may regard it as, in general terms, a representative of the Dimetian 

 series." The distribution in the district, however, of this class 

 of rock, presuming it to be all of one age, is very much against its 

 being older than the rhyolite. Besides the main mass in the Ercal 

 there are two small patches of it in the midst of the rbyolites near 

 the south-eastern end of the Wrekin, whose mode of occurrence 

 suggests intrusive bosses. At Primrose Hill it is likewise entirely 

 surrounded by the rhyolite, into whicli, indeed, it almost seems to 

 pass, and strongly suggests a neck, to which other phenonu'ua point. 

 Holocrystalline rock also occurs at the extreme N. of the Lawley, 

 where it passes gradually into the rhyolite. Similar rock is referred 

 to by Dr. Callaway near Wallsbank, Cardington Hill. It is here 

 at the edge of the rhyolite, and is cut off by a fault from the 

 Caradoc shales. Some connection may here perhaps be suggested 

 with the porphyry to be presently noted in this hill. 



These isolated occurrences only suf/f/esf intrusion on the part of the 

 eurite (as we may call it), and not on the part of the rhyolite ; but 

 in the Ercal Quarry there is a pretty long line of junction, and 

 this ought to tell us whether there is anv intrusion or nor, and by 



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