Geological Society of London. 137 



garded by the author as belonging to the presumably Archaean 

 massifs of that mountain-chain. In reply, the author stated that 

 he regarded this as a challenge to demonstrate the soundness or un- 

 soundness of the hypothesis to which he had committed himself. 

 The present paper gives the result of his investigations, undertaken 

 in the month of July, 1889, in company with Mr. James Eccles, 

 F.G-.S., to whom the author is deeply indebted for invaluable help. 

 The paper deals with the following subjects : — 



(1) The Andermatt Section. 

 By the geologists aforesaid, a highly crystalline white marble which 

 occurs on the northern side of the Urserenthal trough, at and above 

 Altkirch, near Andermatt, is referred to the Jurassic series (mem- 

 bers of which undoubtedly occur at no great distance, almost on the 

 same line of strike). The author describes the relation of the 

 marble to an adjacent black schistose slate, and discusses the signifi- 

 cance of some markings in the former which might readily be con- 

 sidered as organic, but to which he assigns a different origin. He 

 shows that there are most serious difficulties in regarding these two 

 rocks as members of the same series, and explains the apparent 

 sequence as the result of a sharp and probably broken infold, as in 

 the case of the admitted band of Carboniferous rock at Andermatt 

 itself. That the section is a difficult one on any hypothesis the 

 author admits; but after a discussion of the evidence, he concludes 

 that " that tendered on the spot demands a verdict of ' not proven ' — 

 that obtainable in other parts of the Alps, will compel us to add, 

 ' not provable.' " 



(2) The Schists of the Val Piora. 

 These schists, already noticed by the author in his Presidential 

 Address to the Society in 1886, occur in force near the Lago di 

 Eitom, and consist of two groups : — the one, dark mica-schists, some- 

 times containing conspicuous black garnets, banded with quartzites, 

 the other various calc-mica schists ; between them, apparently not 

 very persistent, occurs a schist containing rather large staurolites or 

 kyanites. On the north side is a prolongation of the garnet-actino- 

 lite (Tremola-) schists of the St. Gothard, and then gneiss; on the 

 south side gneiss. There is also some rauchwacke. This rock, at 

 first sight, appears to underlie the Piora-schists, and thus to be the 

 lowest member of a trough. If so, as it is admittedly about Triassic 

 in age. the Piora-schists would be Mesozoic. The author shows 

 that (1) the latter rocks do not form a simple fold; (2) they are 

 beyond all question altered sediments ; (3) they have often been 

 greatly crushed subsequent to mineralization ; (4) the garnets, 

 staurolites, etc. (if not injured by subsequent crushing), are well 

 developed and characteristic, and are authigenous minerals. 



(3) The Rmtchivacke and its Relation to the Scltist. 

 (a) The Val-Piora Sections. — The author shows that the rauch- 

 wacke, which at first sight seems to underlie the dark mica-schist, 

 is inconstant in jjosition (on the assumption of a stratigraphical 



