762 Geological Society : — 



fused product is powdered, examined with the microscope, and 

 then placed in a diffusion-column, by the use of which errors due to 

 the few small bubbles or unfused mineral-particles, on the few 

 occasions when these exist, are eliminated. The diffusion- column 

 is sealed in a glass tube. Acid rocks were found to increase 

 6 to 10 per cent, in volume, intermediate rocks 5 to 7 per cent., 

 and basic rocks chiefly less than 6 per cent. Of the minerals 

 tested, pargasite underwent the greatest expansion, albite gained 

 10 per cent., while in anorthite and leucite the increase was less 

 than 4 per cent. It is pointed out that this expansion would be a 

 very effective force in the case of the melting of rock-magmas kept 

 solid by pressure. Experiments were also made in order to ascertain 

 the melting-points of the rocks and minerals experimented upon : 

 these were found to range from 1260° C. for rhyolite to 1070° C. 

 for Clee-Hill dolerite. The refractive indices of the glasses were 

 determined in dense fluids. In determining the melting-points of 

 individual minerals, the author's results agree fairly closely with 

 those of Day & Allan, but differ from those of Joly & Cusack. An 

 attempt was made to find experimentally the eutectic proportions 

 of quartz and felspar. It Avas found impossible to reproduce in the 

 laboratory the conditions which, in nature, seem to have existed 

 during the formation of pegmatites. On the other hand, a mixture 

 of orthoclase and albite gave a melting-point lower than those of 

 either mineral taken separately. 



March 27th.— Sir Archibald Geikie, L.C.L., Sc.D., Sec. R.S., 

 President, in the Chair. 



The following communications were read : — 



1. ' On the Southern Origin attributed to the Northern Zone in 

 the Savoy and Swiss Alps.' By Prof. T. G. Bonnev, Sc.D., LL.D., 

 P.R.S., F.G S. 



Prof. Lugeon, with some other eminent Continental geologists, 

 explains certain peculiar flat folds, the higher of which sometimes 

 project considerably beyond the lower, in the more northern sedi- 

 mentary zone of the Swiss and Savoy Alps, by supposing that to 

 no small extent the strata have been thrust forward from an 

 original position south of the watershed of the Pennine-Lepontine 

 Alps; overriding, as they advanced, their crest and that of the 

 Oberland (neither having then attained its present altitude). This 

 pressure Avas produced by the greater thickness of deposits of 

 Mid-Tertiary age, speaking in general terms. Prof. Sollas, in 

 concluding a very interesting and suggestive paper on some 

 experiments with cobbler's wax, published in the last volume of 

 the Quarterly Journal of the Society, p. 716, suggests that the 

 results are favourable to the views of the Lausanne professor. 



The author takes exception to some of the cases, especially two 

 to the east of the Simplon Pass, which are adduced by Prof. Lugeon 

 in support of his hypothesis, pointing out that he has confused 

 an ordinary with a crystalline limestone, and merely schistose 



