3 6 FRA NK DAWSON ADA MS 



One of the most interesting granite contacts seen on the 

 excursion was reached from Payole, that, namely, of the Cirque 

 d'Arbisson. Leaving Payole early in the morning on August 13th 

 the party made their way through the Bois d'Arreiou-Tort and up 

 over the moraines mantling the valley bottom and the lower 

 slopes, and after several hours climbing reached the foot of the 

 great Cirque. But little rock is exposed on the way up, but at 

 the Cirque itself, whose walls tower up in the form of a great 

 amphitheater of bare rocks skirted with talus piles, the expo- 

 sures are magnificent. (See Fig. 5.) 



The rocks composing the Cirque are Upper Devonian in age 

 and consist of thinly banded strata, greatly contorted and 

 twisted, and now converted into hornstones of several kinds, 

 varying in character with the original composition of the rock. 

 The unaltered rock was not seen, but it would seem to have been 

 not unlike that worked in the quarries near Payole. The argil- 

 laceous bands, however, were probably more numerous and some 

 of the bands were highly siliceous. The contortions and the 

 breaking apart of the harder bands with flowing of the relatively 

 softer layers, in this case the limestones, between the fragments 

 is excellently seen. (See Fig. 6.) The original marly beds 

 have been converted into epidote hornstones, while the more 

 siliceous beds are converted into a flintlike material which is 

 much darker in color. Some of the limestone bands, although 

 greatly contorted, have retained their fine-grained texture and 

 blue color, but owing to the shearing movements to which they 

 have been subjected they have assumed, as is frequently the case 

 in such occurrences, a sort of schistose structure. The limestone, 

 however, is usually traversed by little streaks, coarser in grain 

 and whiter in color, marking the first stage of a recrystallization 

 and passage into marble. The limestones or calcareous bands 

 in places contain large crystals of red garnet, resembling the 

 well-known occurrences on the Stikine River, although the 

 development of the crystals is not so perfect. Beautiful flat 

 rosette-like groups of vesuvianite crystals also occur in places 

 along the bedding planes, usually between the layers of epidote 



