92 Reports and Proceedings — Oeohgical Society of London. 



cai-inal space wliicb. occurs in all known Jurassic " Glabra3." The 

 escutclieon is remarkably large and possesses transverse rugte, 

 as in the Neocomian " Quadratas." The author regarded the species 

 as a transition form connecting the two groups of Trigonice above 

 mentioned. The description of the new species was accompanied 

 by a note on the Purbeck strata of the Vale of Wardour by the 

 liev. W. E. Andrews. 



IL— Jan. 5, 1881.— Eobert Etheridge, Esq., F.E.S., President, in 

 the Chair, — The following communications were read : — 



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

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

 some of the Eocks, by Prof. T. G. Bonney, M.A., F.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 2;one, about Bodafon, 

 Llangwyllog, Llanerchymedd, and Paris Mountain, which, he 

 considers, establish the following conclusions : — (1) that in 

 Anglesey there are two Archeean groups, the slaty and the gneissic ; 

 (2) the slaty is composed of slates, shales, limestones, grits, con- 

 glomerates, 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 horn- 

 blendic schists, grey gneiss, quartz-schist, and halleflinta; (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. 

 Davids volcanic group, the Charnwood rocks and the Lilleshall 

 series than with the Bangor group • (5) the slaty series is un- 

 doubtedly Pebidian, the gneissic series may, with some probability, 

 be referred to the Dimetian. The microscopic structure of the 

 principal varieties of the rocks mentioned 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. Tbe author showed that while the flaggy 

 (upper) schists dip uniformly to N.E., the limestone dips in a very 

 variable manner E.S.E., E., and but rarely N.E., any dip N. of E. 

 being exceptional, and then only at a distance from the schist. 

 Again, the Smoo mass of limestone, cut off from the Durness area by 

 a faulted strip of gneiss, dips either E.S.E,, or even more to S. 

 After discussing the relation of the quartzite and gneisses, the author 

 passed to the Assynt district, and pointed out that the relations of 

 the limestone and the quartzite are by no means satisfactorily 

 established, that their conformity is rendered dubious by a marked 



