286 



NATURE 



[July 20, 1893 



Judd, F. R. S. The author proposed to apply the term "com- 

 posite dyke " to any fissure which contains two or more distinct 

 varieties of igneous rock, differing from one another in chemical 

 composition or mineralogical constitution. Such dykes fall 

 into two classes : — (l) Dykes in which differentiation has evi- 

 dently taken place in the materials after their injection, as in 

 the examples described by Dr. Lawson in Canada and by Prof. 

 Vogt in Norway. (2) Dykes in which there is evidence of the 

 reopening of the fissure after its first injection and the introduc- 

 tion of materials of totally different composition. It is this 

 class of dykes of which such interesting illustrations are found 

 in Arran. These Arran dykes belong to the latest volcanic 

 eruptions of the British Islands ; their analogues are found alike 

 in the south of Scotland, and in the north of England and of 

 Ireland. They are the infilled fissures along which sporadic 

 volcanic outbursts took place after the extinction of the great 

 volcanoes of the Inner Hebrides. The subaerial products of 

 these later, and, for the most part, insignificant volcanic erup- 

 tions, have been all swept away by denudation, except at Beinn 

 Hiant and the Sgur of Eigg. The materials filling these dykes 

 belong to two totally different classes — one distinctly basic, 

 with about 55 per cent, of silica ; and the other markedly acid 

 in composition, with from 65 to 75 per cent, of silica. The 

 basic rock is an augite-andesite, which passes sometimes into an 

 intersertal and occasionally into an ophitic dolerite (tholeite 

 and diabase) ; the glass of this rock shows a great tendency 

 to separate from the phenocrysts. The acid rock is often a 

 highly vitreous material ("pitchstone " or " pitchstone-por- 

 ])hyry ") which by devitrification passes into various forms of 

 felsite and quartz-felsite. These rocks, if we class them ac- 

 cording to the nature of the porphyritic minerals they contain, 

 fall into the several groups of vitrophyric and trachytoid lavas, 

 to which the terms pantellerite, quartz-pantellerite, rhyolite, 

 andesite, and dacite have been applied. The glassy groundmass 

 in the whole of these rocks, however, is always abundant and its 

 characters are remarkably uniform however much the phenocrysts 

 may vary. The author pointed out that, while the peculiarities of 

 the first class of composite dykes can be accounted for by selective 

 crystallisation and liquation going on within the m.igma which 

 has been injected into the dyke, no such explanation is sufficient 

 in the case of the composite dykes of the second class. That the 

 association of two totally different rocks in the same dyke is 

 not accidental, the numerous and varied examples at Tormore 

 sufficiently prove. Where, as in these cases, it is found that 

 there is the greatest dissimilarity between both the crystals and 

 the glassy groundmass of the two rocks, the differentiation has 

 taken place in the magma, prior to its injection into the dykes, 

 and before the work of crystallisation had commenced. Prof. 

 Bonney, Mr. W. W. Watts, Mr. Hulke, and Mr. Teall took 

 part in the discussion on the paper, and the author briefly re- 

 plied. — Notes on an intrusive sheet of diabase and associated 

 rocks at Robin Hood, near Bassenthwaite, by J. Postlethwaite. 

 The positions of the outcrops of the igneous rock were de- 

 scribed, and a grit-band was recorded as running parallel to the 

 diabase. The diabase, and vein-stuff associated with it, have 

 furnished antimony, lead, copper, and arsenic ; and the same 

 ores, with the exception of the last two, were also found in 

 minute grains in the grit. Analyses of the grit and diabase 

 have been made by Messrs. Hellon and Brockbank. Prof. 

 Bonney has examined slides submitted by the author, and 

 allowed his notes to be used in the paper. The igneous rock 

 has produced slight metamorphism in the surrounding rocks of 

 the Skiddaw Slates. — On two dinosaurian teeth from Ayles- 

 bury, by R. Lydekker. Two teeth from the neighbourhood of 

 Aylesbury, believed to be of Portlandian age, were referred to 

 the sames species as a tooth figured by De La Moussay from 

 the Portlandian of Boulogne. The Aylesbury teeth were 

 described, and the nature of the animal which posses.sed them 

 was discussed. — On a new plesiosaur from the Waipara River, 

 New Zealand, by Capt. F. W. Hutton, F.R.S. This specimen 

 was shortly described by Sir James Hector in 1873. The 

 author considered it more prudent to follow Mr. Lydekker in 

 referring all the known New Zealand Cretaceous 

 Sauropterygians to Leidy's genus Cimoliosaurus, and he there- 

 fore described this form as a new species of that genus. — 

 Observationson the affinities of the genus ^j/n;<ra;«!a, by Robert 

 F. Tomes. Researches recently made by the author relative 

 to the structure of certain undoubted Astrocania of the 

 Gosau beds, having for their primary object the better understand- 

 ing of the supposed species of the genus obtained from the Glamor- 



NO. 1238, VOL. 48] 



ganshire conglomerate, have been productive of results which will 

 render a complete modification in the classificatory position of 

 the genus imperative. The author gave a new definition of the 

 genus, in which he did not include any species of an earlier date 

 than the cretaceous period, all the so-called Jurassic Astrocanice 

 being referable to other and quite distinct genera. — Description 

 of a new genus of Mcuireporaria from the Sutton Stone of South 

 Wales, by Robert F. Tomes. In the Quarterly Journal for 

 1885 is a detailed description of a coral from the Sutton Stone 

 named Astrocania gibbosa. This specimen is not the type of 

 the species, and a re examination of it by the author has proved 

 that it is not an Astrocccnia. Two other specimens have also 

 been examined, and as a result of examination of the three the 

 author is enabled to found a new genus Styloseris, of which a 

 diagnosis was given, and the specific name gibbosa was retained 

 for this, the only known species. The genus will take its place 

 near Clausastraa, from which it differs by possessing a well- 

 developed columella and increasing by both fissiparity and 

 gemmation. Mr. Etheridge and Dr. G. J. Hinde took part in 

 the discussion that followed. — Study of the dykes of Hope, 

 Idaho, by Herbert R. Wood. A description was given of the 

 geographical distribution and characters of acid and basic dykes 

 traversing slates and quartzites along the northern shore of Lake 

 Pend'Oreille, Idaho, accompanied by notes on the glaciatiou of 

 the area. The microscopic features of the igneous rocks were 

 also described. — The rise and fall of Lake Tanganyika, by 

 Dr. Robert Sieger. The author referred to Mr. Carson's paper 

 on the same subject in the Society's Journal for 1892. He him- 

 self believed the oscillation of level to be analogous to variations 

 reported as occurring in other African lakes, and to be due to 

 climatic change. He brought forward evidence in favour of 

 the coincidence of change of level and climatic change, but did 

 not believe that his views are by any means contradictory to 

 those of Mr. Carson, for the phenomena may be explained by 

 a combination of the influences of climate with those of 

 mechanical agencies. — On Cheilostomatous Bryozoa from the 

 Middle Lias, by Edwin A. Walford. The author described 

 some forms of bryozoa from the spinatus-zoite of the Middle 

 Lias near Banbury, some of which had previously been classed 

 with the Cyclostomata. The new material not only shows the 

 opercular aperture but the opercula in situ, together with 

 appendages and supra-oral ovicells characteristic of the Cheilo- 

 stomata. In addition he also found giant cells (cistern-cells^ of 

 form quite dissimilar from the ordinary zocecia and probably 

 reproductive. He cited M. Jules Haime as having described 

 in his magnificent monograph somewhat similar cells from the 

 Inferior Oolite ; and in the Oxfordshire Great Oolite bryozoa 

 Mr. Walford found cistern-cells like the Lias species on some 

 colonies like Diastopom. He contended that it is merely the 

 acquisition ot very well-preserved material which is needed to 

 show the necessity of removal of many such species to the 

 Cheilostomata. The name Cisiernophora was suggested for the 

 genus, of which several forms were described. 



Royal Microscopical Society, June 21. — The Rev. 

 Canon Carr in the chair. — Dr. J. E. "Talmage, of Salt Lake 

 City, Utah, exhibited and gave an account of some specimens of 

 selenite found in the interior of a mound at South Wash, near 

 Fremont River, Utah. As a rule, portions of selenite useful for 

 optical purposes are measured by inches and weighed by ounces, 

 but here he had found some which weighed 1000 lbs. The 

 formation around the mound was mostly sand and clay, and thj 

 region bore everywhere strong evidences of weathering, by 

 means of which the mound had been weathered out into re- 

 lief. He had removed some twenty tons of the crystals, 

 amongst which were many single crystals, measuring 4 to 5 

 feet in length, and entirely perfect, the most regular being 

 4 feet long with faces of 6 inches. One fine crystal, 5 feet 

 long, had no less than nineteen small ones jutting out from it ; 

 twins and groups were also very common. Inclusions of 

 sand, clay, and liquid were often present. He believed this 

 to be a unique formation. — Mr. G. C. Karop read a letter on 

 the subject of diseased beard-hairs. — Prof. T. Jeffrey Bell read 

 a letter from Capt. Montgomery on the subject of chicken- lice, 

 ticks from grass, and other parasites found in Natah — Dr. Nias 

 read a paper on the development of the Continental form of 

 microscope. — A discussion ensued, in which Dr. Dallinger, Dr. 

 Braidwood, Mr. Karop, Mr. Teasdale, and the author took 

 part. — Mr. C. Rousselet gave a risumS of his paper on Floscu- 

 laria pelagica and other new rotifers. 



