590 



NA TURE 



[Oct. 20, 1887 



subsequently adopted the report. Now I submit with the utmost 

 respect, but with the greatest earnestness, to those here 

 assembled, that a course of physiological physics to be delivered 

 in the new College of Science would iie a real boon to all 

 students of medicine, whether they had succeeded in obtaining 

 their diploma or not. The human body is a mass or congeries 

 of separate machines, susceptible of mechanical explanation ; 

 but, setting aside the heart and lungs, already named, how 

 many students have their attention specially drawn to Donders's 

 and r.andoli's optical researches on the eye and eyesight, or 

 to Helmholtz's account of the mechanism of the ear? Such a 

 course, moreover, would in no way clash with other" courses 

 given elsewhere on different branches of the same subject, and 

 it would eminently fulfil the exact purpose even to the very 

 words of the great man whom we are to-day met to com- 

 memorate." 



THE BRITISH ASSOCIA TION. 

 Section C — Geology. 



Preliminary Note on Traverses of the Western and of the 

 Eastern Alps made during the summer of 1887, by Prof. T. G. 

 Bonney, F.R. S. — The first traverse was made along the line of the 

 Romanche from near Grenoble to the Col du Lautaret, and 

 thence by Brianfon over the Mont Genevre and the Col de 

 Sestrieres to Pinerolo, at the edge of the Italian plain. The 

 second went from Lienz, across the central range of the Tyrol 

 to Kitzbiihel, and the rocks of this range were also investigated 

 at other places. During both traverses the author had the 

 advantage of the assistance of the Rev. E. Hill, who had 

 accompanied him on a similar journey in 1885. The results of 

 their examination fully confirm the views already expressed by 

 the author as to the nature and succession of the crystalline i^ocks 

 of the Alps. 



(i) The lowest group consists partly of modified igneous rocks 

 (which indeed occur at all horizons), partly of gneisses of a very 

 ancient (Laurentian) aspect. 



(2) The next group, up to which there seems a gradual 

 passage, consists mainly of more friable gneisses and moderately 

 coarse mica-schists (Lepontine type). This group is commonly 

 less fully developed in the above districts than in the Central 

 Alps, having probably been removed by very ancient denuda- 

 tion. 



(3) The third group has an enormous development. It forms 

 a large part of the Cottian and Graian Alps, and it flanks the 

 central axis of the Eastern Alps on both sides, often passing 

 beneath the ranges of Secondary strata which here form the 

 northern and southern ranges. It has been traced almost with- 

 out interruption from east to west for more than 50 miles on 

 the southern and 80 on the northern side of the central 

 range. It has a very close resemblance in all respects to the 

 uppermost group of schists in the Central Alps, found to some 

 extent in the Lepontine and yet more largely in the Pennine 

 Alps, and the author fully agrees with the Swiss and Austrian 

 geologists in regarding it as in the main a prolongation of the 

 same series. It is characterized especially by rather dark- 

 coloured mica-schists, often calcareous, sometimes passing into 

 fine-grained crystalline limestones, with occasional intercalated 

 chloritic schists, especially in the lowest part and with (rarely) 

 quartz schists. 



(4) The Carboniferous and Secondary strata infolded or over- 

 lying in the Western Alps section, and the Palaeozoic (? Silurian) 

 and Secondary strata succeeding the metamorphic rocks in the 

 Eastern Alps, are comparatively little altered and are each 

 readily to be distinguished from the above. 



(5) The succession of strata in the third group is inexplicable 

 unless it be due to stratification ; in the second this explanation 

 appears highly probable ; and in the first not more difficult than 

 any other. 



(6) As groups of rocks with marked lithological characters 

 occur in like succession over a mountain chain measuring above 

 400 miles along the curve, and sometimes at distances of 40 miles 

 across it ; and as these groups correspond with rocks recognized 

 as Archaean elsewhere, which exhibit like characters and some- 

 times a like order of succession, the author thinks a classification 

 of the Archaaan rocks by their lilhological characters (using 

 the phrase in a wide sense) may ultimately prove to be 

 possible. 



(7) The views already expressed by the author as to the dis- 

 tinctness of cleavage-foliation and stratification-foliation hare 

 been fully confirmed by the examination of the above districts. 

 He believes that the failure to recognize this distinction is the 

 cause of the contradictory statements with regard to the relation 

 of foliation and bedding which have been made by so many 

 excellent observers, and lies at the root of much of the confusion 

 which exists on the subject of the so-called metamorphic rocks. 



The Origin of Banded Gneisses, by J. J. H, Teall. — The 

 author first discussed the meaning of the term gneiss. This 

 term was generally understood to denote a more or le s foliated 

 rock of granitic composition. Dr. Lehmann had proposed, how- 

 ever, that it should be used in a structural sense only, as meaning 

 a more or less foliated plutonic rock. He would thus speak of 

 granite-gneiss, diorite-gneiss, and gabbro-gneiss. The author 

 called attention to specimens illustrating gneissic structures in 

 acid and basic plutonic rocks. When various examples of 

 gneissic rocks — that is, rocks of the composition of plutonic 

 igneous rocks but possessing parallel structures — were compared, 

 two types of parallel structure might be recognized ; the one 

 characterized by a parallel arrangement of the constituents, the 

 other by an arrangement of the constituents in bands of varying 

 mineralogical composition ; thus, bands having the mineralogical 

 composition of a diorite frequently alternated with others having 

 the composition of granite. He proposed to discuss a possible 

 mode of origin for the banded gneisses of the latter type. It 

 was now admitted that those of the former type were largely due 

 to the plastic deformation of masses of plutonic rock either during 

 or subsequent to the final stages of consolidation. 



Many observers were, however, still inclined to believe that 

 those of the latter type conld only be accounted for by supposing 

 that the original materials had accumulated by some process akin 

 to sedimentary deposition. Now a possible mode of origin for 

 these could be found if we could show : (i) that plutonic masses 

 are liable to vary in composition, and (2) that such masses are 

 occasionally deformed either during or subsequent to their con- 

 solidation. Scrope long ago proved that the laminated structure 

 of certain volcanic rocks (Hparites) is due to the plastic defor- 

 mation of heterogeneous masses of acid lava. Any heterogeneous 

 lump if deformed into a fiat sheet will show laminated or banded 

 structures, because each individual portion must of necessity take 

 the form of the entire mass. Scrope not only proved this, but 

 called attention to the similiarity between the structures of acid 

 lavas and those of gneisses and schists. (''Geology of Ponza 

 Isles.") 



The author then proceeded to refer to illustrations of the fact 

 that plutonic masses do vary in composition. He referred to the 

 so-called contemporaneous veins, which are often more acid, and 

 to the concretionary (?) patches which are often more basic, in 

 composition than the main mass of the rock with which they are 

 associated. He also referred to cases in which granite and diorite 

 may be seen to vein each other in the most intricate manner, and 

 especially drew attention to the photographs taken at the 

 Lizard last year illustrating this feature. If complex masses of 

 the kind referred to were deformed after the fashion of the acid 

 lavas described by Scrope, then banded and puckered gneissic 

 rocks would necessarily result. He then showed that in the 

 Lizard district the banded rocks of Prof. Bonney's "granulitic 

 series" were continuous with masses in which granitic and 

 dioritic rocks could be seen to vein each other in the most in- 

 tricate manner, and that the constituent bands of the granulitic 

 series were composed of rocks petrologically identical ^»ith those 

 of the igneous complex. He did not mean to imply that the 

 deformation was connected with the intrusion of the plutonic 

 masses. He was rather inclined to regard it as due in th^^J 

 majority of cases to mechanical forces acting posterior to co^HI 

 solidation. The uncertainty which might exist as to the precis^pl 

 conditions under which the deformation was affected did not in- 1 

 validate the main conclusion, which was that a banded structure 

 in rocks having the composition of plutonic igneous rocks was 

 no proof that the latter were not of igneous origin. 



On the Occurrence of Porphyritic Stnicttires in some Pocks of 

 the Lizard District, by Howard P"ox and Alex. Somervail. — 

 Prof. Bonney has described a porphyritic diabase which is seen 

 on the shore at Polpeor ; it cuts, in an intricate manner, through 

 micaceous and hornblendic schists. The authors have traced this 

 rock further, and have recognized a porphyritic structure not only 

 in many dykes and intrusions along the coast which cut through 

 the serpentine, but also in the darker bands of Prof. Boar""" 



