Geological Society. 151 



interspersed throughout the book, and the author's sources of in- 

 formation duly acknowledged. But, owing to the abstruse nature 

 of the subject, this treatise only addresses itself to the learned in 

 Mathematics, and will for the most part be perfectly unintelligible 

 to the ordinary student of science. 



XXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 74.] 



January 5, 1881. — Eobert Etheridge, Esq., E.E.S., President, 

 in the Chair. 



THE following communications were read : — 

 1. "The Archaean Geology of Anglesey." By C. Callaway, Esq., 

 M.A., D.Sc, E.G.S. With a Note on the Microscopic Structure of 

 some of the Eocks, by Prof. T. G. Bonney, M.A., E.E.S., Sec.G.S. 



The author discussed the stratigraphy and lithological characters 

 of the rocks in the following areas : — The border of the Menai Strait, 

 the Llangefni region, and the central zone about Bodafon, Llan- 

 gwyllog, Llanerchymedd, and Paris Mountain, which, he considers, 

 establish the following conclusions : — (1) that in Anglesey there 

 are two Archaean groups, the slaty and the gneissic ; (2) the slaty 

 is composed of slates, shales, limestones, grits, conglomerates, and 

 chloritic schists, in which at present a definite order has not been 

 ascertained (the gneissic group is composed of the following, in 

 descending order — granitoidite, chloritic and hornblendic schists, 

 grey gneiss, quartz-schist, and halleninta) ; (3) the slaty series is 

 occasionally foliated, but is usually in a partially altered state ; the 

 gneissic group is thoroughly metamorphosed ; (4) the slaty series 

 has closer lithological affinities with the St. -David's volcanic group, 

 the Charnwood rocks, and the Lilleshall series than with the Bangor 

 group ; (5) the slaty series is undoubtedly Pebidian, the gneissic 

 series may, with some probability, be referred to the Dimetian. The 

 microscopic structure of the principal varieties of the rocks men- 

 tioned in the above paper was described by Prof. Bonney. 



2. " The Limestone of Durness and Assynt." By C. Callaway, 

 Esq., D.Sc, F.G.S. 



This paper gave the result of an examination of the vicinity of 

 Durness and Inchnadamf, where Lower- Silurian fossils occur in a 

 limestone, as discovered by Mr. C. Peach. At Durness the only 

 evidence of the limestone underlying the schist is the asserted fact 

 of the dip being in the same direction ; for all admit the junction 

 to be a faulted one. The author showed that while the flaggy (upper) 



