TRANSACTIONS OF SECTION C. 705 



The author considers further the gradual diminutiou of the crenitic process seen 

 in the later periods of Archaean time, and its feehler manifestations in Palaeozoic and 

 more recent ages down to the present. lie notes, moreover, that as the result of 

 geographical changes, erosion and partial deposition alike disturbed the succession 

 of the later groups of crenitic rocks, none of which can claim that universality and 

 uniformity which belong to the oldest known group, the fundamental granitoid 



The author concludes with a brief sketch of the great divisions of the indige- 

 nous crenitic rocks recognised by him, from the most ancient granitic substratum 

 to the Taconian series, which appears to be the last of the characteristically crys- 

 talline indigenous groups, it being, so far as known, succeeded directly by the un- 

 crystalline Cambrian, or the equally uncrystalline Keweeniau, which may not, 

 improbably, be itself included in the lower part of the Cambrian series. 



4. Freliminarij Note on, Traverses of the Western mid of the Eastern Alps made 

 during the Summer of 1887. By Professor T. G. Bonnet, D.Sc. LL.D., 

 F.B.8., F.O.S. 



The first traverse was made along the line of the Romanche from near Grenoble 

 to the Col du Lautaret, and thence by Brian^ou 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 Kitzblihel, 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 rocks of the Alps. 



(1.) The lowest group consists partly of modified igneous rocks (which in- 

 deed 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 denudation. 



(.').) 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 without inter- 

 ruption from east to west for more than fifty miles on the southern, and eighty 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 characterised 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 overlying in the 

 Western Alps section, and the Palfeozoic (PSilurian) and Secondary strata succeed- 

 ing the metamorphic I'ocks 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 ; as these groups correspond with 

 rocks recognised as Archaean elsewhere, which exhibit like characters and sometimes 

 a like order of succession, the author thinks a classification of the Archaean rocks by 

 1887. z z 



