358 The Rev. Prof. Blake — Base of the Sedimentary Series. 



— Mr. Harker has shown that on the eastern side it is intrusive 

 in the Ordovician slates ! 



The net result, therefore, at present, of recent work in N.W. 

 Carnarvonshire, is this, that, with the exception of the western side 

 of the Lleyn Peninsula, there is nothing proved to be Precambrian 

 in age. 



4. Malvern. — Of this small area I cannot speak with so much 

 confidence, having never examined it with care. There can now be 

 no doubt that below the ordinary Cambrians there are here two 

 distinct groups of rocks ; one, presumably the younger, according 

 to the account of Dr. Callaway, is so like the Caradoc and Wrekin 

 masses that, in the lack of any direct evidence, its age and relations 

 must be determined by theirs ; and the other, the main mass of schistose 

 crystalline rocks, which, since their description by Dr. Holl, are 

 generally admitted to be of Precambrian age. The absence from 

 among them of any ordinary unaltered sediments, and their intimate 

 connection with igneous masses of a foliated type, renders it 

 probable that they are older than any other rocks in England or 

 Wales, unless it be the equally undetermined Cornish and South 

 Devonshire schists. 



As to their origin, there are two very distinct " views " before 

 geologists. On the one hand, Mr. Eutley regards the main mass as 

 ordinary sediments metamorphosed into schists, and intruded upon 

 after their formation by igneous masses. On the other hand, Dr. 

 Callaway affirms that there are here no sediments at all, but that 

 the whole was originally composed of massive igneous rocks of two 

 distinct types, which interpenetrated each other in veins. These 

 veins were then drawn out by shearing, and where this process was 

 carried furthest, the whole rock recrystallized and produced the 

 ordinary schists. 



Without a detailed knowledge of the district, which might afford 

 some independent criterion, one can only choose between these 

 two accounts on general principles. It appears we may divide 

 the rocks into three categories ; the massive crystalline rocks, 

 schistose rocks in the neighbourhood of these, and schists with no 

 visible connection with igneous rocks. About the first of these 

 there is no question. That shearing and resulting schistosity 

 and mineral change may be demonstrated in some cases belonging 

 to the second category seems proved by Dr. Callaway's observations ; 

 but that the schists and gneisses away from all obvious igneous masses 

 are reconstructed out of the disintegrated materials of such masses 

 would seem to require more proof than the apparent passage of such 

 schists into those of the second category. Moreover, Mr. Eutley 

 describes part of these schists as quartzites with rounded particles, 

 and others as containing fragments of felspars — phenomena which 

 would be impossible on Dr. Callaway's explanation. It would 

 appear from this, that no single explanation will cover all the 

 foliated rocks of the Malverns — and that the separation of those of 

 one origin from those of another has yet to be worked out. 



5. Shropshire. — According to the mapping of the Survey, and the 



