42 W. M. Hutchings — Clays, Slates, and Contact- Metamorphism. 



hotel. It is a moderately altered slate, containing a good deal of 

 quartz. Biotite has formed in considerable amount, but the quartz 

 is still distinctly clastic. No sign of felspar is seen, and there are 

 here no " spots." B is from a point about three-quarters of a mile 

 away up the stream, almost the highest exposure in the Beck, and 

 about 300 to 400 yards away from the outcrop of the granite. How 

 near it may be to the actual contact cannot be stated, because we do 



not know the contour of the granite underground ; but it is certainly 

 not very far away from it. The rock is here very completely 

 " regenerated ; " not a particle of original quartz remains, felspar 

 is abundant, and there are many spots of various kinds. 



It will be noted that B is unusually rich in alkali for a slate, 

 though the figures can be closely paralleled by those of some 

 other published analyses. So far as can be judged from the appear- 

 ance of the rocks and their relationship to the line of strike, the 

 two specimens represent the same slate. 



There is nothing in the analyses, in spite of the increase of nearly 

 3 per cent, in the total alkalies, to justify any inference that a 

 transfer of material has taken place from the granite to the slate. 

 The balance of the accumulated evidence on this question appears to 

 show that such transfer is either non-existent or very rare, except 

 perhaps at the actual junction, and the above analyses are quite in 

 harmony with this. Slates and shales are known to vary considerably 

 in composition, within very moderate distances, in the same layers. 

 A is much more calcareous and also more ferruginous than B, and 

 this causes the main difference. It will also be noted that the 

 proportion of potash to soda is almost identical in both cases, a fact 

 which speaks strongly against the idea of the introduction of any 

 alkali from an external source. 



Concerning the question of newly-formed felspar in contact-slates, 

 etc., it is to be remarked that more recent observations tend to show 

 that its occurrence is not by any means so rare as was at one time 

 supposed. This fact is emphasized by R. Beck, in a paper in which 

 he records his own observation of felspar in the contact-rocks of the 

 Elbe Valley (Tschermak's Min. and Petrog. Mittheilungen, p. 13, 

 1893), and refers to a list of other notices of similar occurrences. I 

 may state that having myself of late very carefully examined 

 specially prepared slides of a good number of contact-slates, etc., from 

 various places on the Continent, I have found them to contain felspar 

 in frequent instances, its occurrence not having been previously 



