18 GREEN MOUNTAINS IN MASSACHUSETTS. 



From the above description it will be seen that the actual nature of 

 the relation of the limestone to the rotten schist was hidden. But just west 

 of where the contact should be I found the limestone conformably overlain 

 by a few feet of Hoosac schist, Farther east is a small shaft, from which 

 was hoisted some of the rock excavated between the western headings of 

 the "west" shaft and the open cut; this rock is a more or less rotten calca- 

 reous feldspathic mica-schist, having- the same elongated structure parallel 

 to the axes of the folds as in the rotten transition schists of this zone, and 

 marked by the same similarly arranged long, narrow flakes of mica. It 

 recalls in structure, also, at once, the calcareous gneiss associated with the 

 limestone on its eastern border near South Adams, and also the noncalca- 

 reous and rather less feldspathic mica-schist of the "Buttress" core. I 

 think that, taken in connection with the facts observed south and east of 

 Cheshire hill, we have in this rock the upward transition from the quartzite 

 to the limestone brought to the tunnel line in an anticlinal arch, and that 

 we have, in the wholly decomposed material of the former open cut, the 

 lateral transition from the rest of the limestone into the Hoosac schist. A 

 few hundred feet, from east to west, would span the whole lateral passage 

 from limestone to Hoosac schist. This transitional calcareous schist decom- 

 poses much more easilv than the limestone and is therefore more rarely 

 seen. Nevertheless, as stated above, it is found exactly where it should 

 occur as such a transitional form, not only in the western end of the great 

 tunnel, but at several points along the western base of Hoosac mountain 

 above the quartzite and west of the infolded schists. 



While the rocks of the zone of lateral transition, in the horizon of ver- 

 tical transition from quartzite to limestone, were tolerably hard, they suc- 

 cumbed to disintegrating agents much quicker than the quartzite proper. 

 But the rocks of the zone of lateral transition between the limestone and 

 Hoosac schist, being calcareous schists, were adapted to the most rapid 

 destruction, and we therefore find them only where the conditions for their 

 preservation have been exceptional. 



From Cheshire hill northward this zone covered anticlinal folds turned 

 over to the west, which have been to a great extent eroded down to the 

 harder beds towards the true quartzite. It does not seem improbable that 



