384 A. VVINC'HELL — RESULTS O] LRUHEAN STUDIES. 



the mica and hornblende schists the proportion of mica scales generally 

 increases, and in some states the graywacke has much the aspecl of a fine, 

 earthy mica Bchist. The appearance suggests thai we have a rock in which 

 the mica clement is jusl emerging into existence from Borne magma or is 

 checked in its emergence before attaining full development This is what I 

 have frequently denominated "nascent micaschist." It answers the descrip- 

 tion of the " tender mica schists" which characterize Hunt's " Montalbau 

 series," which, so far as 1 know, may occupy nearly the same horizon. Quite 

 a development of this formation occurs about the mirth end of White [ron 

 lake. 



In the passage downward from nascent mica schist to the truly crystalline 

 schists, we sometimes arrive at a stadium in which minute and obscure de- 

 velopments of both biotite and hornblende may be detected. One almost 

 fancies the primitive ground material to have been in a condition of petro- 

 genic equilibrium. The impression is deepened by noting the predominance 

 of biotite at one point and the predominance of hornblende at another, 

 almost in the same hand specimen. These zones of doubtful supremacy are 

 narrow. In the immediate vicinity, some older bed reveals the presence of 

 characteristic biotite Bchist or hornblende schist. 



At many points the transition from the semi-crystalline to the crystalline 

 >chi>ts is made without the intervention of graywacke. A very noteworthy 

 instance <<\' this occurs on the north shore of ( iunllint lake,* where the ver- 

 tical porphyrellitic argillites approach the gneissic area. At several points 

 on the lake shore the rock is observed to develop the feldspar crystals 

 which characterize porphyrel. Occasionally it develops quartz grains in- 

 stead, ami constitutes w hat is described near Vermilion lake as " porphyritic- 

 ally quartzose porodite." In the transition belt here alluded to this con- 

 dition of the rock receives also occasional dun or dark structureless patches. 

 These, farther on, assume a uralitic aspecl and then a hornblendic aspect, 



and out of them emerge, in zones still nearer the gneissic area, > (times 



uralitic hornblende individuals which, with quartz and feldspar already pres- 

 ent, give a uralitic gneiss. Sometimes also the dark patch'.- develop mien. 

 and in Buch case the ultimate formation is a good gneiss. The ground ma- 

 teria] gradually diminishes and finally ceases to appear. 



A variation of the mode of transition may he Been at the same locality. 

 In this is an intervention of uralitic schist. The Bemi-crystalline schist 

 I . • • -_ r 1 1 1 - as a sericitic or porphyrellitic argillite. It then becomes porphyrel, 



wing harder and more crystalline. Next, the feldspar is Been to weather 

 reddish, while the rock ha- a Byenitic look. Still farther toward the gneissic 

 area the formation ig banded by belts looking like hornblende Bchist; hut 

 the hornblende is still of argil li tic softness, and there are line glistening 



