546 



SCIENTIFIC NEAVS. 



[June 8, l8 



British Islands." He said that the area within which 

 volcanic action manitested itself during the tertiary period 

 in this country was not absolutely and regularly definable, 

 but it went from northern Yorkshire right across to the 

 west of Donegal, and from the northern part of the Lews, 

 down the west of Scotland to the centre, and from the 

 Minch right away down to the south of Antrim. They 

 could divide this history into episodes, and the most 

 tremendous volcanic action was that which produced the 

 basic dykes. Altogether, they had a line of volcanic 

 material somewhere about iSo miles in length, showing 

 itself in this form. All through the dyke region they 

 found two remarkable types of protrusion — the single or 

 solitary series, and the gregarious. The first type of 

 dykes ran through all kinds of rocks, sometimes rising to 

 the surface, and maintained a wonderful parallelism right 

 across the country from sea to sea. They were not so 

 thoroughly basic as those of the second type. He men- 

 tioned a block of basalt on the coast of Mull as an example. 

 The second type of dykes was by no means so persistent ; 

 they were not so broad or so long, nor so regular or 

 parallel, as the first. Sometimes they were separated by 

 many miles from their neighbours, but sometimes they 

 were crowded all together in a single mass. If they 

 examined them they could be divided into at least two 

 groups. There were those that ran from south-east to 

 north-west. They began at the Cleveland dyke, and went 

 northwards to the Grampians. These dykes all belonged 

 to one period, as might be seen from their uniformity, 

 from the way in which they radiated from one common 

 centre, and from the way in which they cut into the for- 

 mations with which they were associated. The second 

 group crowded together in districts, and were found in 

 the basin of the Clyde, in Islay, Jura, Mull, and Skye. 

 The great problem that presented itself was what had 

 been the history of these dykes, and how they had come 

 to be where they were. He attributed their existence to 

 the action of the lava, which forced itself up underneath 

 the region of the dykes. The ground was thus arched 

 over, and a horizontal tension cracked the whole country. 

 The lava then solidified and formed the great parallel 

 dykes. But that was only the beginning of a very long, 

 complicated, and interesting series of processes. Dr. 

 Geikie divided the area into four plateaus, pointing out 

 the characteristics of each, and stated that from the 

 evidence they had they were driven to suppose that there 

 was not one central vent in each of the plateaus, but 

 many vents. Dr. Geikie concluded by giving an indica- 

 tion of the composition of the materials of these dykes. 



GEOLOGICAL SOCIETY. 

 At the meeting held on May 33rd, Mr. W. T. Blandford, 

 LL.D., F.R.S., President, in the Chair, the following 

 communications were read : — 



" On the Spheroid-bearing Granite of Mullaghderg. 

 Co. Donegal." By Frederick H. Hatch, Ph.D., F.G.S. 

 Communicated with the permission of the Director- 

 General of the Geological Survey. 



This paper deals with a remarkable variety of granite 

 which may be compared with the well-known orbicular 

 diorite or Napoleonite of Corsica. According to Mr. J. R. 

 Kilroe, of the Geological Survey of Ireland, who first 

 discovered this interesting rock, the concretionary balls 

 occur in close juxtaposition in a mass of granite of five 

 or six cubic yards in size. They have not been found 

 in any other portion of the granite area. 



The author first gave a detailed description of the 

 microscopic structure of the normal granite. It is a 

 coarse-grained rock, composed essentially of quartz, 

 orthoclase, microcline, oligoclasc, greenish hornblende, 

 and black mica. Sphene is an accessory consti- 

 tuent. Since it contains no white mica, the rock be- 

 longs to that subdivision of granite which has been 

 termed graniliie. A description of the spheroidal bodies 

 was then given. The balls are somewhat flattened, the 

 greatest diameter being in one case four inches, the 

 smallest three. Each ball consists of two distinct parts, 

 a pinkish central portion (the nucleus) and a dark-coloured 

 peripheral or zonal portion (the shell). The nucleus 

 consists of an irregular granitic aggregate of oligoclase 

 felspar with a little interstitial quartz. The peripheral 

 shell is composed chiefly of oligoclase, but also contains 

 abundant included plates of biotite, and over 12 per 

 cent, of magnetic iron-ore. It is to the presence of the 

 last-mentioned mineral that the zonal portion owes its 

 dark colour. 



The conclusion the author arrived at from a considera- 

 tion of the subject was, that concretionary bodies occur- 

 ring in granite, may, according to the mode of arrange- 

 ment of their constituents, be divided into three classes, 

 viz : — 



1 . The coiicrelionaiy patches of Phillips. 



2. The granosphentes of Vogelsang. 



3. The bclonosphcrites of Vogelsang. 



The Spheroids from Mullaghderg belong to the last- 

 mentioned class. They must be regarded as concretions 

 formed during the consolidation of the granite magma, 

 by a process of zonal and radial crystallisation around 

 an earlier-formed nucleus. 



" On the Skeleton of a Sauropterygian from the 

 Oxford Clay, near Bedford." By R. Lydekker, Esq., 

 B.A., F.G.S. 



A description was given of a considerable portion of 

 the skeleton of a Sauropterygian from the Oxford Clay 

 of Kempston, consisting of several upper teeth, most of 

 the mandible (of which the symphysial region is entire), a 

 considerable number of vertebra; mainly from the " pec- 

 toral " and dorsal regions, the greater portion of the two 

 pelvic, and fragments of the pectoral limbs, and a con- 

 siderable proportion of the pectoral and pelvic girdles. 

 These remains were referred to Plesiosaurus pliilarchus, 

 Seeley, and the various parts described in detail. 



The author discussed the advisability of retaining the 

 forms described by various generic names by Professor 

 Seeley, under the name of Plesiosaurus, and stated his 

 intention of employing the latter term in its widest sense 

 for the present. With this definition, the form under 

 consideration was shown to present characters inter- 

 mediate between those of Plesiosaurus and Pliosaurus, 

 but was retained provisionally in the former genus. 

 Although a direct link in the chain connecting the two 

 genera, P. pliilarchus was not regarded as an ancestor of 

 Pliosaurus, since teeth undistinguishable from those of 

 the latter genus occur in the Coralline Oolite. 



Finally it was concluded that the evidence brought 

 forward was sufficient to render necessary the abolition 

 of the name Plios::urida;, and the inclusion of Plesio- 

 saurus and Pliosaurus in a single family. 



" On the Eozoic and Patezoic Rocks of the Atlantic 

 coast of Canada in comparison with those of Western 

 Europe and the Interior of America." By Sir J. W.- 

 Dawson, LL.D, F.R.S., F.G S. 



