1865.] MACFARLANE — GEOLOGICAL SKETCH OF ROSSIE. 267 



GEOLOGICAL SKETCH OF THE NEIGHBORHOOD 

 OF ROSSIE. 



Br Thomas MacFarlane. 



Having in April last spent nearly a week in and around Rossie, 

 St. Lawrence County, State of New York, and made some obser- 

 vations which appear to me of importance in connection with the 

 economic minerals occurring there, I have thought myself justified 

 in attempting briefly to describe the relations of the rocks and ore 

 deposits of this interesting locality. This has no doubt been 

 already done to some extent by the officers of the Geological 

 Survey of the state of New York, and I should not probably have 

 ventured on this sketch had I not satisfied myself of the exis- 

 tence, in the district to which it has reference, of certain zones 

 of rock which in Norway are termed "fahlbands," and which are 

 found there to exercise a very important influence on the contents 

 of mineral veins. In a paper contained in vol. vii. of this Journal, 

 I gave a full description of these fahlbands, the presence of which 

 in the Laurentian rocks affords another proof of the identity of 

 that series with the Primitive Gneiss of Scandinavia. 



The rocks which occur in the neighbourhood of Rossie belong- 

 almost exclusively to the Laurentian formation. Here and there 

 the gneissoid rocks are unconformably overlaid by patches of 

 Potsdam sandstone, and the latter rock most likely at one time 

 covered the whole area of the district, but has since been removed 

 by denudation. The following are the principal rocks which occur 

 in the neighbourhood of Rossie, and which belong to the Primitive 

 Gneiss or Laurentian formation : 



Gneiss, both micaceous and hornblendic. The feldspar, quartz, 

 and mica in the former sort, are often intimately combined with 

 each other in bands of considerable thickness. Quite as frequently, 

 however, the mica with a smaller quantity of feldspar and quartz 

 forms narrow bands alternating with other bands destitute of lami- 

 nation, and consisting of a coarsely granular mixture of feldspar and 

 quartz ; so that this gneiss in reality is a compound of very mica- 

 ceous gneiss and pegmatite. The micaceous varieties of the 

 gneiss occur principally to the south and southeast of the village of 

 Rossie, while that of a hornblendic character is principally developed 

 on the north and west. It is worthy of remark that while the feldspar 

 in the micaceous gneiss is for the most part white, in the horn- 

 blendic variety it is reddish coloured. On the road to Depeyster 



