332 Reports and Proceedings — Geological Society of London. 



diabases." There is also among them a felsite-breccia with micro- 

 pegmatite developed in the cracks. 



He considers that nearly all the igneous rocks of Cntch have been 

 derived from a single magma, which in a solid condition must have 

 contained large crystals of augite, olivine, and ilmenite in a ground- 

 mass of lime-felspars, and have been throughout of a basic character. 

 Such a magma originated in more than one centre. One was possibly 

 not far from the Sindree basin, whence lines of weakness diverged. 

 Along these, owing to the thickness of the strata, there was no 

 extrusion at the surface, and laccolite-domes were formed. Where 

 the rock reached higher levels, it spread out into sheets between the 

 domes and aided in the production of synclinals. Another centre 

 was west of Bhuj, where the rock reached the surface without 

 materially disturbing the sedimentary rocks, and formed the so-called 

 " stratified traps." There were also areas here, especially to the 

 south, where escape was impossible and domes were formed. 



The author observes that his conclusions, if correct, may be 

 applied to explain the source of the Deccan trap without eruptive 

 centres. It may have been forced out from innumerable orifices as 

 from a sieve, none of these being so much larger than others as to 

 make a definite centre. 



IL— June 9, 1897.— Dr. Henry Hicks, F.R.S., President, in the 

 Chair. The following communications were read : — 



1. " The Cretaceous Strata of County Antrim." By W. Eraser 

 Hume, D.Sc, F.G.S. 



The paper, which deals with the Irish Cretaceous strata, is divided 

 into four parts. 



(1) This contains a detailed account of the principal subdivisions, 

 their local distribution and characteristic fossils. The area occupied 

 by these rocks is separated into five divisions, each marked by 

 special lithological and palceontological features. These are — 

 (a) The Southern Division, extending from Moira to Lisburn. 

 Here the highest zone of the Chalk, that of Belemnitella mucronata, 

 rests directly on the Ti-iassic strata, the junction-bed containing large 

 pebbles, associated with the above-mentioned species, (b) The 

 Central Division, mainly including the sections between Lisburn 

 and Belfast. All the main lithological features are here displayed, 

 namely : (i) Glauconitic Sands (a blue-green rock rich in glauconite) ; 

 (ii) Glauconitic Marls ; (iii) Yellow Sandstones (a light calcareous 

 sandstone) ; (iv) Chloritic Sands and Sandstones of the ^a;o^?/racoZit?n6a 

 zone (yellow-green sands and sandstones) ; and (v) White Limestone. 

 Under No. iii Tate and Barrois both included the zone rich in 

 JrtocerawiMs-fragments occurring in the next division, but this zone 

 is difi'erent in colour and chemical composition, and is practically 

 absent in the Central area, the White Limestone with conglomeratic 

 or nodular chalk at the base resting unconformably on the lower 

 beds. Paleeontologically, all these lower beds are rich in large 

 dimyarian bivalves, especially Trigonics, Area, Cucullcea, etc. 



