1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 247 



until you reach the depression in the high ridge where the track 

 passes into the Grisons, and the crest is there so narrow and ele- 

 vated, that we positively sat upon the peaks of flysch with one leg 

 in the Grisons and the other in Glarus. Widening to about 100 

 feet or more to the south-west of the mountain-path, this flysch is 

 then directly surmounted by a mass of hard grey subcrystalline lime- 

 stone (x) (about 150 feet thick), which is perforated by a natural 

 tunnel or hole*, and hence the name of Martin's-loch. This lime- 

 stone is, as far as my eye could discern (and it commanded several 

 miles both to the east and west), continuously superposed to the 

 flysch in varying and irregular thicknesses, and more or less in a 

 tabular position, over a great area, including the peaks of Hanstock, 

 Linterberg, and Karpfstock. M. Escher had, indeed, sedulously fol- 

 lowed the range, and had found in it Jurassic ammonites near the 

 Karpfstock. Now, this limestone is in its turn distinctly overlaid by 

 a zone of talc and mica schist (y), in parts having quite the aspect of 

 a primary rock. This uppermost rock, according to M. Escher, is 

 an integral part or continuation of the Sernft conglomerates and 

 schists which are seen in the adjacent vale of Wallenstadt to lie be- 

 neath the whole secondary series. Before I made this section, I 

 had supposed that the younger and nummulitic deposits might be 

 simply plastered up on the sides of the older rocks, and not really 

 pass under them. But the examination of the lofty and narrow 

 ledge I had traversed checked such hypotheses, for on both sides 

 of it I witnessed the same relations. Again, I tried to imagine, that 

 without any inversion of the strata, metamorphism had here seized 

 upon all the upper strata to the exclusion of the lower ; but this 

 speculation was equally fruitless ; for, independently of the proof 

 obtained by M. Escher, that the overlying limestone contained ammo- 

 nites, that rock is quite unconformable to the flysch on the edges of 

 which it reposes irregularly. I was also well assured from pretty 

 extensive observation, that no such rock existed in any part of the 

 supracretaceous series. In descending from the summit-ridge into 

 the valley of the Vorder Rhein in the Grisons, I had, indeed, another 

 and an independent proof, that the rocks underlying the solid lime- 

 stone, with its cover of talc schist, were really of supracretaceous 

 age, for we found in them both nummulites and the same teeth of 

 fishes which characterize the flysch in many other tracts. At this 

 point the fossiliferous "flysch" beneath seemed to be quite uncon- 



* M. Escher informs me that the superposition of the Jurassic rocks to the 

 niimmulitic extends to the Rosenlair mountain, in the canton of Bern, and to the 

 Grisons. In the canton Glarus he has found the same relations to range from 

 Martin's-loch to the Panix pass, where crystalline schists, equally resting on the 

 limestone in question and on nummulite rocks, are further surmounted by a 

 limestone with Pentacrinites, and resembling the modified inferior oohte and lias 

 of these regions. If ever, therefore, it should be attempted to explain away the 

 anomaly of Martin's-loch (as M. Escher well observes in a letter to me), by sup- 

 posing that its enigmatical limestone and overlying chlorite schists are mere modi- 

 fications of true overlying ''flysch" on Jura limestone, still the superposition of 

 the pentacrinite hmestone to the whole of the series is inexplicable except on the 

 supposition of a complete overthrow " en masse." 



