142 Correspondence — Mr. C. Callaway. 



felsite pebbles in which couie from the same source. Lastly, he showed 

 that the signs of the metamorphism and apparent " melting down " 

 asserted to be visible on the sides of Llyn Padarn, proved, on micro- 

 scopic examination, to be mainly superficial. Hence, he maintained 

 that these rocks were rhyolitic lava-flows of Pre-Cambrian age. 



5. " On the Metamorphic Series between Twt Hill, Caernarvon, 

 and Port Dinorwic." By the Eev. Prof. T. G. Bonney, M.A., F.R.S., 

 F.G.S., and F. T. S. Houghton, Esq., B.A. 



In the Geological Survey Map this district is coloured as " intru- 

 sive felsite," together with those spoken of in the last paper. It 

 was asserted to be probably metamorphic rock by Prof. Hughes and 

 Dr. Hicks in a communication made to the Society last year, and 

 the first author confirmed that view by microscopic examination of 

 a specimen collected by them. The authors had during the past 

 autumn more minutely examined the district, and found : — (1) that 

 the general character of the series was that of a metamorphic one ; 

 (2) that the rocks of granitoid aspect were associated with well- 

 marked beds of conglomerate ; (3) that this series extended up to a 

 little beyond Port Dinorwic, where the quartz-felsite set in. The 

 paper described the microscopic structure of some of the rocks, and 

 the authors expressed the opinion that the more granitoid specimens 

 were probably the results of alterations of felspathic grits. 



cozRie-iEsiPODsnDiEiisrciE. 



THE TRIPARTITE DIVISION OF THE SILURIAN AND CAMBRIAN 

 FORMATIONS. 1 

 Sir, — "Will you allow a still small voice from the frontiers of 

 Siluria to say a word on Mr. Lapworth's proposal to call the rocks 

 of the Second Fauna Ordovician ? The lines have fallen to me in 

 the pleasant places of South Shropshire, amidst the monuments of 

 Murchison's genius. But Murchison is gone, the surveyors are 

 gone (it is to be hoped they will come back again), and I am left 

 almost alone to represent Caer Caradoc and Wenlock Edge. By the 

 names of Murchison and Sedgwick (now, perhaps, in still happier 

 hunting-grounds, recounting their old exploits, and wondering at 

 their ancient squabbles), I implore the rival schools to accept the 

 olive-branch ! He who holds it is worthy to propose the compromise. 

 Moffat and Girvan have witnessed his renown. Scores of faults and 

 flexures testify to his skill. He has won an Ordovicia in the Scottish 

 Uplands. Let true scientific frontiers be established ! Let Barrande 

 and Hughes meet together ; let Cambria and Siluria recede from each 

 other ! 



I am bound to record my humble protest against the present 

 imbroglio. The want of a proper name for the rocks of the second 

 fauna is most embarrassing. I have used " Lower Silurian " under 

 protest, and " Cambro-Silurian " with dissatisfaction. Working some 

 time ago amongst the Upper Cambrians of Salop, and being anxious 



1 This and the two following letters have been unintentionally delayed in 

 publication. — Edit. Geol. Mag. 



