﻿The Waldensian Gneisses. 241 



(Engadine) some masses of compact green schist are seen, inter- 

 calated in a rather crushed gneiss. They prove to be intrusive dykes 

 modified by pressure. Microscopic examination of specimens from 

 these reveals no trace of any definite structure indicating an igneous 

 rock ; a slice, cut from one of the masses within an inch or so of a 

 junction, shows it to be a foliated mass of minute chlorite or 

 hydrous biotite, with granules of epidote (or possibly some sphene) 

 and of a water-clear mineral, perhaps a secondary felspar. An actual 

 junction shows a less distinct foliation and some approach to a 

 streaky structure. A slide from the middle of another dyke (about 

 18 inches thick) exhibits a more coarsely foliated structure and 

 minerals generally similar to the last, except that it may contain a 

 little actinolite and granules of haematite (?) and the clear mineral, 

 in some cases, seems to be quartz. The structure and most of the 

 minerals appear to be secondary. Chemical analysis shows the rock 

 to have been an andesite. A specimen from a third dyke is generally 

 similar, but is rather less distinctly foliated. 



A somewhat similar, but rather larger intrusive mass by the side 

 of the Lago Bianco shows more actinolite and signs of primary felspar, 

 with other minerals. Here the rock retains some likeness to a 

 diabase. The resemblance of certain of these rocks to somewhat 

 altered sediments is remarkable. The Author considers the bearing 

 of this evidence upon other and larger masses of ' green schist ' 

 which occur in the Alps, and expresses the opinion that their 

 present mineral structure may be the result of great pressure acting 

 on more or less basic igneous rocks. 



2. ' The Waldensian Gneisses and their Place in the Cottian 

 Sequence.' By J. Walter Gregory, D.Sc, F.G.S. 



The lower part of the sequence of the Cottian Alps has been 

 universally divided into three series, of which the lowest has been 

 regarded as a fundamental (basal) Laurentian gneiss. It is the 

 object of the present paper to show that this rock is really intrusive 

 in character and Upper Tertiary in age. The writer endeavours to 

 show this by the following line of argument: — (1) The gneiss con- 

 sists of only isolated outcrops instead of a continuous band, and these 

 occur at different positions and not always at the base of the schist 

 series ; (2) the gneiss is intrusive, because : (a) it includes fragments 

 of the overlying series instead of vice versa, (b) it sends off dykes of 

 aplite into the surrounding schists, (c) it metamorphoses the rocks 

 with which it is in contact, and (d) the schists are contorted near 

 the junction ; (3) the gneisses are further shown to be later than 

 the igneous rocks intrusive into the ' pietre verdi ' series, as these 

 never traverse the gneiss. 



No positive opinion as to the age of the overlying schists is 

 expressed in the paper, though it is pointed out that the recent dis- 

 covery of radiolarian muds in the series may necessitate their 

 inclusion in the Upper Palaeozoic. The freshness of the gneisses, 

 the fact that these have not been affected by the early Tertiary 



Phil. Map. IS. 5. Vol. 38. No. 231. Aug. 1894. R 



