ANNrVERSART ADDRESS OF THE PRESIDENT. 79 



valley down a gorge chiefly consisting of a coarse gneiss followed 

 by strong mica-schist. 



The investigations which I have described extend over an area 

 measuring about 85 miles from W.S.W. to E.jN'.E., and full 50 miles 

 in a transverse direction. It would be easy for me to quote corro- 

 borative evidence from other districts in the Alps, but this, I think, 

 Avill suffice to warrant the following conclusions : — 



(1) The oldest rock visible in the above- described districts of 

 Alps is a granitoid gneiss, which gives no evidence of bedding or 

 foliation other than such as may be only the result of subsequent 

 pressure, and which may itself possibly be a rock of igneous origin. 

 It does not, however — as do certain other granitoid rocks in the 

 same region, of a rather different lithological character — exhibit any 

 indications of intrusion that I have been able to discover, but seems 

 to pass up into 



(2) Finer-grained gneisses, more rapidlj^ varying their character, 

 themselves occasionally showing a foliation and a mineral banding 

 which it is difficult to attribute to any subsequent modification, and 

 apparently interstratified with true mica-schists, and even with 

 crystalline limestones. 



(3) Schists and gneisses, generally rather micaceous, form the next 

 group. The gneisses, which appear to beloug rather to the lower part, 

 are commonly somewhat friable; the felspar occurs in small ill- defined 

 granules, and is of porcelain -white colour ; under the microscope it 

 is less abundant than we should expect from macroscopic examina- 

 tion. Hence this rock differs much, both in the field and under the 

 microscope, from the gneisses of the preceding group. The schists 

 belong rather to the upper part ; mica is the dominant mineral, and a 

 white mica is frequent as well as black ; but chloritic and other green 

 schists occur, while garnet and actinolite are locally abundant, as 

 are cyanite, staurolite, and andalusite. Possibly some of these last 

 should rather be included with the next group, namely 



(4) Schists of a markedly bedded aspect, sometimes micaceous, 

 sometimes (though more locally) chloritic, actinolitic, or talcose, inter- 

 bedded with calc-schists, crystalline limestones, or dolomites (gene- 

 rally slightly micaceous), quartz-schists, and schistose or impure 

 quartzites, all having a marked stratified aspect, but distinctly 

 metamorphic. Thus, as it seems to me, stratification is probable in 

 (2), and becomes absolutely certain before the end of (3). 



(5) Where rocks of different mineral characters suggest by their 

 association that they were originally stratified, the minor banding of 

 the constituent minerals and the arrangement of platy or acicular 

 minerals is generally parallel with the apparent planes of bedding ; 

 that is, there appears to be a connexion between stratification and 

 foliation. 



(6) While a foliation may be produced by a pressure in a crystal- 

 line massive rock, or in one previously foliated, this, in the latter 

 case, though occasionally the dominant, is generally the subordinate, 

 structure, i.e. the cleavage-foliation does not, as a rule, obliterate 

 the stratificatio7i-foUation (see figs. 1, 2, p. 97). 



