May 15, 1884] 



NA TURE 



65 



is assigned, and as regards the period, will be found from Ginzel's 

 numbers to be — 



days 



For Jupiter ... ... -799-16 



Saturn - 27-27 



Uranus - 7'53 



Neptune ... ... - 276 



These figures show a total acceleration of S3672 days, and 

 hence the most probable epoch of the next perihelion passage is 

 found to be 1S86 December 16 -9 G.M.T. 



After remarks upon the physical observations made in 1815, 

 and Bessel's observation of a nearly central occultation of a star 

 by the comet on April 26, we have extensive sweeping ephemer- 

 ides to facilitate the rediscovery at the approaching return ; the 

 places are given for every tenth degree of the sun's longitude, 

 and of the true anomaly from - 120° to +120 . In view of the 

 uncertainty in the length of the comet's period, it may be well 

 to commence the search in 1S85. 



In a supplement Ginzel examines the effect of the attraction 

 of the smaller planets Mercury, Venus, the Earth, and Mars 

 from March 1815 to February 1S17 ; also the possible effect of a 

 resisting medium : these are found to be too small to be worthy 

 of consideration practically. 



The elements assigned by Ginzel's investigation for the 

 comet's next appearance are : — 



Perihelion passage, 1SS6 December 16-9338 Berlin M.T. 



THE BUILDING OF THE ALPS 1 

 II. 

 T PASS now to the section of the Simplon. On the southern 

 side, deep in the glen of the Doveria, in the vicinity of the 

 gorge of Gondo, we find a mass of granitoid gneiss, which recalls to 

 mind that already described from the wildest portion of the upper 

 valley of the Reuss. We may, I think, with confidence affirm 

 that, whatever be the true nature of this rock, we are again 

 touching the foundation-stones of the rock masses of the Alps. 

 As we approach Algaby, the granitoid gneiss becomes more dis- 

 tinctly bedded and variable, a thin band of micaceous crystalline 

 limestone is passed, and presently the more rapid ascent of the 

 pass begins. Hence to beyond the summit we traverse, so far 

 as can be seen, a great series of bedded gneisses, often coarse 

 and even porphyritic, and of schists. The same are displayed in 

 the crags of Monte Leone on the east and of the Rossbodenhorn 

 on the west. As shown in Prof. Renevier's valuable section, 

 bands of crystalline dolomitic limestone, and of hornblendic and 

 garnetiferous schists occur in various places on either side of the 

 Simplon road. Then, after descending about half way to Brieg, 

 we strike the group of the Lustrous Schists, with the usual cal- 

 careous zone in the lower part. Prof. Renevier does not attempt 

 to unravel the complexities of the strata which compose this 

 portion of the central ridge of the Alps, and I feel that my 

 slighter knowledge makes caution yet more imperative ; but I 

 think we are justified in asserting that we have evidence of an 

 upward succession from the coarse granitoid fundamental gneisses, 

 through more variable and bedded gneisses, to a group which 

 recalls the garnetiferous schists, so finely developed on the 

 southern flanks of the St. Gothard — a group also traceable in 

 the upper portion of the Binnenthal, though apparently far less 

 perfectly developed. I think also that in the gigantic anticlinal 

 of the Simplon we have evidence of sharp flexures on a great 

 scale ; and that these garnetiferous schists are only here and 

 there preserved as the lower ends of infolded loops, so that the 

 bulk of the massif, and, so far as I can tell, the actual summit 

 ridges of the Rossbodenhorner and Monte Leone, are composed 

 of the bedded gneisses and strong schists, and perhaps of the 

 more friable gneisses which have been already described in the 

 mountains further to the east. 



The mountains further west — the aspiring peaks which rise 



1 Lecture by Prof. T. G. Bouney, D.Sc, F.R.S., Pres.G.S., at the Rojal 

 Institution, April 4. Continued from p. 46. 



around the two branches of the Visp, including among them some 

 of the highest summits of the Alps, such as Monte Rosa, the 

 Mischabelhorner, the Matterhorn, and the Weisshorn — offer indeed 

 magnificent sections, but are full of difficulty. The fundamental 

 gneiss, if I mistake not, is occasionally exposed — as, for ex- 

 ample, in the rocks of Auf der Platte, at the base of Monte 

 Rosa ; and in parts of the Mischabelhorner blocks of coarse 

 granitoid rock, often very porphyritic, which I refer to the same 

 series, are brought down by the glaciers. There are also mica 

 schists in plenty, such as the summit rocks of Monte Rosa and 

 the backbone — if the phrase be permitted — of the Mischabel- 

 and Saaser hbrner, which I refer to the second zone already de- 

 scribed — that of the bedded gneisses and strong mica schists. I 

 have also seen specimens which closely resemble the garnetiferous 

 schists of the St. Gothard district, but we meet in this district 

 with a group of rocks which, if not altogether unknown before, 

 appear now to be developed to an exceptional extent, and to 

 become an important factor in the Alpine crystalline series. 



Those who are familiar with the environs of Saas and Zermatt 

 will remember how frequently schists or schistose rocks of a 

 greenish colour occur. Sometimes they are interbedded with 

 strong mica schists, or schisty quartzites, sometimes they form 

 homogeneous masses of considerable extent. It is possible that 

 some of the latter are intrusive masses of serpentine, to which 

 subsequent pressure has given a schistose aspect ; certainly 

 there are occasional masses of coarse gabbro, which I think 

 undoubtedly an intrusive igneous rock ; but still, making all 

 allowance for such cases, there is in this region a considerable 

 mass of greenish hornblendic, talcose, and serpentinous rocks 

 which appears to be non-igneous in origin. We find these all 

 around Zermatt. They form the ridges of the Gorner Grat and 

 of the Hornli. They break out through the snows of the Breit- 

 horn and Little Mont Cervin, and constitute no inconsiderable 

 portion of the mighty obelisk of the Matterhorn. The whole ot 

 that peak, according to the investigations of Sgr. Giordano — and 

 with this my own recollections correspond — consists of an appa- 

 rently regularly bedded series of serpentinous and micaceous 

 schists, and of greenish gneisses, with the exception of a gabbro, 

 developed on the western side, which I have no doubt is an 

 intrusive rock. Can we trust these indications ? Are we justi- 

 fied in assigning to this zone, with those characteristics, a vertical 

 thickness of more than a mile ? To these questions I can give at 

 present no answer, further than to state that I am convinced that, 

 notwithstanding the apparent regularity of the bedding in this 

 and the neighbouring peaks, there are really great folds which 

 patient scrutiny may at length unravel, and that this zone of 

 greenish rocks — for which Alpine geologists have proposed the 

 name of Pictra Verde group, appears to underlie the garneti- 

 ferous series of silvery mica schists, and either to overlie or 

 replace the upper portions of the banded gneiss series which 

 succeeds to the fundamental series. 



I do not propose to weary you further with the details of 

 Alpine sections, except that I must add a few words upon the 

 extent of this remarkable series to which I have now introduced 

 you. On the northern side of the watershed in the Swiss Alps, 

 so far as I am aware, it is not generally strongly developed, 

 except in certain localities in the southernmost of the three 

 ranges which make up the whole chain, but in parts of the Tyrol 

 it is well displayed. It borders — the mica schists sometimes 

 dominating — the fundamental gneiss in the Oetzthal massif ; it 

 forms the peak of the Gross Glockner ; it meets us on the Brenner 

 Pass and elsewhere overlain by and folded up with rocks which, 

 if my memory do not mislead me, are the equivalents of the 

 Lustrous Schists of more western districts. 



Again, it is finely developed, seemingly in succession to bedded 

 coarser gneiss, in some of the peaks of the Bernina range, and it 

 occupies a considerable tract about the heads of the valleys to the 

 south. It may be traced, indeed, over a great zone, and with 

 but slight interruption all along the southern slopes of the Alps, 

 even to the south of the head waters of the Po, forming many of 

 the grandest peaks in the Graian, Tarentaise, Maurienne. and 

 Cottian Alps ; and we find traces of it overlying^ the coarse 

 granitoid series in the massif oi the Alps of Dauphine. 



Sections, indeed, in the neighbourhood of Biella, accord- 

 ing to Gastaldi and Sterry Hunt, exhibit the Pietra Verde 

 group overlying the upper or more bedded portion of the 

 great gneissic or basal series, and succeeded by the group of 

 friable gneisses, described above as closely associated with the 

 garnetiferous schists, in a manner that suggests an unconformity. 

 Under ordinary circumstances we should not hesitate to admit 



