220 Dr. C. Callaway — Notes on MetamorpMsm. 



Padarn contain numerous pebbles of the very rhyolite into which they 

 are supposed to pass. It is therefore impossible that the igneous 

 rock, being older than the Cambrian, can have melted it up. Similar 

 evidence is furnished in the Caernarvon area. Thus we see that the 

 cause of the alleged progressive metamorphism being proved non- 

 existent, one branch of the argument breaks down. But, of course, 

 metamorphism may be produced by an agent which is to us invisible, 

 and we are brought to the inquiry : Does this progressive metamor- 

 phism exist? Can we (1) connect the Llanberis beds with their 

 (alleged) equivalents at Bangor, and (2) those at Bangor with their 

 (alleged) equivalents on the other side of the Straits ? I unhesitatingly 

 affirm that no such connection can be established. The Bangor 

 region has been worked by Professors Bonney and Hughes ; but I 

 have seen enough of the ground to be able to form an independent 

 opinion on the question. The area between the " porphyry " mass 

 south of Bangor and the undoubted Cambrian rocks which come in 

 near the city is occupied by a fragmental series of very varied 

 character. The most marked types are agglomerates, felspathic 

 grits and slates, the materials being either derived from the 

 "porphyry,' or consisting of volcanic ejectamenta. Even the slates, 

 under the microscope, are shown to be made up of volcanic dust. 

 Some of the grits are undistinguishable from typical volcanic rocks 

 of the VVrekin. On the Survey Map, the lower part of the Bangor 

 series is represented as partially metamorphosed, presumably on the 

 ground that the rocks bear some resemblance to the contiguous 

 "porphyry," But the similarity is simply due to the fact that the 

 conglomerates and grits are largely composed of pebbles and lapillas 

 of volcanic rock. There is no progressive metamorphism, for there 

 is no metamorphism at all in either group. The " porphyry " is an 

 igneous rock, and the clastic series, being younger, cannot have been 

 altered by it. 



Crossing the Menai Straits-, we find ourselves suddenly landed in 

 a truly metamorphic region. Around us are chloritic and horn- 

 blendic schists, underlain by thin-bedded grey gneiss, the whole 

 lying in foliation planes which have undergone intense contortion. 

 These rocks forca a band about three miles wide, and strike to the 

 south-west. They are too well known to need further description. 



These, then, are the three terms of our series, (1) Clay -slates ; 

 (2) Volcanic agglomerates and tuffs ; (3) Schists and gneisses. The 

 Llanberis slates pass through the state of volcanic ejecta into gneiss 

 and schist ! I presume that in these pages the mere statement of 

 this hypothesis is a sufficient refutation-. 



Cases of an Apparent Passage betiueen rochs of the Ordovician and 

 Caledonian groups in the Northern Highlands. 



I have much pleasure in supplying the followers of Murchison 



with some excellent material for refuting the views of Professor 



Lapworth and myself on the Highland succession. Some of these 



facts are indicated in my recent paper, ^ but its scope did not permit 



1 Quart, Journ, Geol, Soc. August, 1883. 



