296 PROF. T. G. BONNEY ON ilESOZOIC ROCKS AND [Aug. 1 894, 



slope is formed of a dark lead-coloured limestone and a slaty rock 

 or phyllite (as is shown in fig. 3), above which, at a height of 

 some 200 feet above the pass, the gneiss, being as nsual rather 

 micaceous and crushed, makes its appearance. 



The testimony of these sections and such evidence as can be 

 obtained by a general inspection of the district appear to me to 

 justify the following conclusions : — 



(i) That the belt of rock, admittedly Mesozoic, varies considerably 

 in breadth. 



(ii) That the strata of which it consists are neither abnormal in 

 character nor more metamorphosed than is usual in a disturbed region 

 with rocks of this age in the Alps. 



(iii) That the rauchwacke is the soft, dusty, yellowish limestone 

 which is found at the base of the Mesozoic rocks in dozens of localities 

 between the longitudes of Olivone and Visp 1 on both sides of the 

 watershed of the Alps, and occurs, as is so often the case, in irregular 

 interrupted patches. 



(iv) That the Altkirche marble (including the more quartzose and 

 micaceous varieties) occurs in a very uncertain fashion, sometimes 

 twice, sometimes once, sometimes not at all, and its thickness is 

 certainly variable. 



(v) That in one or two sections it undoubtedly passes into more 

 micaceous and more quartzose schists, which correspond in all their 

 essential characters with members of the crystalline series 2 in other 

 parts of the Alps. 



(vi) That there is clear proof of the Altkirche rock having under- 

 gone, after it became a marble, much mechanical disturbance, 

 apparently similar in amount to that which has affected the adjacent 

 Jurassic limestones. 



(vii) That there is nothing to suggest that the exceptional con- 

 dition of the marble may be due to ' contact-metamorphism,' and 

 that the rock is practically indistinguishable from micaceous marbles 

 which, elsewhere in the Alps, pass into calc-mica- and other schists 

 and form part of the crystalline series. 



Thus it appears that the evidence before us does not give an 

 absolute demonstration of the age of the Altkirche marble. I have 

 failed to find, on the one hand, a clear transition from it to the 

 Jurassic rock, on the other a distinct unconformity between them or 

 indubitable fragments of the former in the latter. Facts may be 

 quoted for and against either hypothesis. That which affirms the 

 marble to form part of the same system as the Jurassic rocks seems 

 at first sight the more simple and more accordant with the field 

 evidence in any single section ; but, if it be adopted, we must confess 

 ourselves unable to support the interpretation by evidence from other 



1 I restrict myself to regions where I have myself examined it during the 

 last ten years. 



2 Those which I have elsewhere called the ' upper schists.' 



