September 28, 1893] 



NA TURE 



dust could convey explosions should be repeated. It was to be 

 noted in drawing conclusions from laboratory experiments, that 

 Che conditions obtaining in the mine were more favourable to 

 ihe production of explosions, the temperature being higher and 

 the air drier and denser. In conclusion he showed that the 

 anticipated evils resulting from watering the mine do not occur. 



Mr. Hall, in the course of his remarks, said the higher the 

 quality of the coal, the greater was the liability to explosion. 

 He hoped that it had been proved to the satisfaction of practical 

 people that coal-dust and air alone were competent to produce 

 explosion. 



Prof. Thorpe said that in an explosion caused by flour-dust, 

 which had reduced a mill to a heap of dislocated bricks, he 

 had received an object lesson, which had quite converted him 

 to the coal-dust theory. Experiment had shown him that coal- 

 dusts varied greatly in their capacity of exploding ; some will 

 not explode under any conditions, while others he could at any 

 time explode with certainty. 



Mr. Stokes declared himselfin favour of the second of the three 

 opinions mentioned by Prof. Dixon. It should not be concluded 

 that large amounts of gas could not rapidly accumulate in pits. 

 In one mine, in which for four years no gas had been found, an 

 evolution of gas took place which in twenty-five minutes was 

 sufficient to fill the workings. The lamps being good, no explo- 

 sion took place ; had it done so, all the evidence would have been 

 in favour of its origin being due to coal-dust. He looked for 

 remedial measures in improved explosives and safety-lamps, rather 

 Chan in watering, which he considered insufficient to more than 

 moisten the surlace of the dust, unless carried to an imp'rac tic- 

 able extent. Others having spoken, mainly in favour of the 

 coal-dust theory, Prof. Dixon, in reply, said that he was glad 

 that all mining engineers now seemed to recognise the dan- 

 gerous character of coal-dust. 



After the above discussion. Prof. Smithells showed by ex- 

 periment that iodine vapour will glow on heating, supporting 

 his contention that the luminosity of flame may be due to in- 

 candescent gas. 



The papers on organic cherai-try read at Nottingham were 

 very few, viz. — "On the Reil Colouration of Phenol," by Dr. 

 C. A. Kohn ; "On the Sails of a new Sulphurea Hase," and 

 "On Citrazlnic Acid," by W. J. Sell and T. H. Eisterfield ; 

 and "On Ethylbutane Teiracarboxylate and its Deiivatives," 

 by Bevan Lean. In the course of the latter investigation two 

 isomeric modifications of di-benzyl adipic acid have been ob- 

 tained. The Report of the Committee on Isomeric Naph- 

 thalene Derivatives was read. The work done has been 

 chiefly in connection with the orientation of mixed nitro and 

 halogen <lerivatives. 



The following pieces of apparauis were described, viz. — An 

 Apparatus for Extraction for Analysis of Gases dissolved in 

 water, by Edgar B. Truman, and a new form of Bunsen and 

 Roscoe's Pendulum Actinometer, by Dr. Richardson and J. 

 < luick. 



GEOLOGY AT THE BRITISH ASSOCIATION. 

 /~\UT of the sixty papers contributed to this year's meeting of 

 ^^ Section C. a considerable number, as might have been 

 expected from the personal influence of the President, Mr. 

 Teall, were on subjects connected with Petrology. Amongst 

 this series, two of the most important were read by the emin- 

 ent foreigners Prof. Biii^ger and Prof. Iddings, who had come 

 over especially to attend this meeting. rNext in number were 

 ihe papers on Glacial Geology. The other papers group them- 

 selves into those on Local an4 Triassic Geology, Palajontology, 

 1 oreign Geology, and Vulcanology. 



"On the Genetic Relations of the Ba^ic Eruptive Rocks 



of Gran (Christiana region) " by Prof. W. C. Brogger. — 



This paper dealt with a series of eruptive bosses and 



laccolites forming a line of hills, I'f which the chief, in 



order from north to south, are ^\) IJrandberget, (2) Siilvs- 



■■■S*'. (3) Dign.xs. The main rocK type in these bosses was 



illed by the author Olivine-gabbroiliabase. It is basic (43 per 



cent. SiOj) in I, rather less basic (47 per cent.) in 2, and 



somewhat acid (49 percent.) in 3 ; the more basic rocks were 



j erupted first, then the less and less basic in order from north to 



1 south. From the intimate connection of the minerals in the 



' different types, and the occurrence of all intermediate varieties, 



it was proved that these rocks had segregated in succession 



NO. 1 248, VOL. 48] 



from a magma whose average composition was not unlike tha 

 of the rock of Solvsbergef. The giadation in chemical compo- 

 sition produced a similar gradation in the mineral percentages, 

 the felspar increasing from 12-64 per cent., and the pyroxene 

 diminishing from 67-10 percent, in a southerly direction. The 

 author briefly stated that the contact metamorphism due to these 

 plutonic rocks was quite different in character from that pro- 

 duced by a neighbouring mass of quartz-syenite on the same 

 group of sedimentary rocks. 



The eruptive bosses are accompanied by a great series of 

 dykes and sheets of lampropbyric character, and varying from 

 Camptonite to Bostonite. The author brought forward a 

 quantity of evidence to prove that (l) these two extreme types, 

 with silica percentages ranging from 40-56, had been derived 

 from the same magma ; (2) that 9 parts of Camptonite and 2 of 

 Bostonite (about the proportion observed in the field) would 

 give a magma of the composition of the Olivine-gabbro-diabase 

 of Solvsberget ; (3) that these lamprophyric dykes had been de- 

 rived from the same magma as the plutonic rocks : and (4) that 

 the differentiation had been effected while the maguia still re- 

 mained fluid. It was further shown that the differentiation was 

 probably due to the migration of less soluble constituents to the 

 cooling margin, that the Camptonites had a composition closely 

 allied to that of the brown hornblende of the area, and that 

 while the essential cooling of the plutonic rocks had taken place 

 in the eruptive bosses themselves, the dyke rocks had segregated 

 before extrusion. 



A subsidiary differentiation has taken place in some 

 of the plutonic rocks, giving rise in the more basic Brand- 

 berget to a pyroxenite (with 95 per cent, of pyroxene) and augite- 

 diorite, and in the less basic Solvsberget to pyroxenite and 

 Labrador-porphyrite. 



Other points of importance to be noted were: (l) That 

 under different physical conditions not only various mineral 

 aggregates, but rocks of varying chemical composition had 

 resulted from the crystallisation of the same magma ; (2) that 

 similar products result in this case from the segregation of an 

 Olivine-gabbro-diabase magma, as have elsewhere been derived 

 from a magma that has produced nepheline-syenites ; (3) that 

 the direction of segregation according to laws of crystallisa- 

 tion throws considerable light in the order of volcanic eruptions 

 from neighbouring centres. 



"On the Dissected Volcano of Crandall Basin, Wyoming, ' 

 by Prof. J. P. Iddings. This paper was divided into a strictly 

 petrological portion, and one dealing more broadly with the 

 features of the area, and illustrated by slides brought over for 

 the purpose by Prof. Iddings. The palreozoic and mesozoic 

 deposits, almost unbroken up to the Laramie, had been dis- 

 turbed and eroded before the outbreak of this volcano, now 

 represented by lavas and breccias, penetrated by radiating dykes, 

 and a core of crystalline rock, which is surrounded by a chaotic 

 mass of scoriaceous breccia and massive flows. Erosion has 

 removed at least 10,000 feet from the summit of the volcano, 

 and has cut 4C00 feet deeper into the valleys on either side of 

 the cenire. The lower breccia cuniains several varieties of 

 andesite, the upper is chiefly basahic, which is also the character 

 cf the chief massive flows. The dyke rocks are on the whole 

 more cryslalline, and contain biotite to the almost total exclu- 

 sion of the olivine of the lavas and breccias. The core is chiefly 

 of gabbro, which, however, passes into diorite, and even to 

 aplite ; these highly acid rocks appear to be amongst the latest 

 of intrusions, but are cut by a few dykes of lamprophyric basic 

 rock, which are also represented in the flows outside the core. 

 The author's investigations show that under difi'erent circum- 

 stances totally different mineral aggregates arise from the cool- 

 ing of the same magma. The ba>ahs containing plagioclase, 

 augite, olivine, magnetite, and sometimes hypersthene, the 

 gaobros, plagioclase, augite, hypersthene, and biotite, besides 

 some magnetite, orthoclase, and quartz, with or without horn- 

 blende. Eurther, the coarseness of crystallisation in the core 

 and dykes seems to have been iiioie influenced by the tempera- 

 ture of the sunounding rock than by the pressure to which they 

 were subjected. 



"On Structures in Eruptive Bo-ses which resemble those 

 of ancient Gneisses," by Sir Archibald Geikie. He thought 

 Lehmann's theory of the dynamical origin of foliation might 

 explain granulitic gneisses with thin folia extending uniformly 

 over a large area, but was inadequate to explain coarsely banded 

 masses of irregular composition. These were better compared 

 with the structures visible in the deeper parts of eruptive bosses 



