78 GEOLOGY OF THE SECOND DISTRICT. 



exception of the Adirondacks, some of which are between three and four thousand feet. 

 Crane's mountain, in Warren county, which has been frequently mentioned, is gneiss, except 

 a portion of its base. The wliolc range of the Black or Tongue mountain, between Lake 

 George and Champlain, is gneiss. So also the range passing through the eastern part of 

 Schroon, of whicli Pliaraoh's mountain is a conspicuous peak, is principally composed of tliis 

 rock. 



It is unnecessary to go into a detail of the ranges, and individual mountains composed of 

 this rock. The general prevalence of it has been already stated ; and we have only to notice 

 the particular exceptions which have been made to it, in the different localities, in order to 

 become acquainted with the formation peculiar to different places in the district. 



Gneiss as a mining rock. 



Experience seems to favor the opinion sometimes expressed, that the firm harder rocks are 

 more safely explored than the soft shaly ones ; but whether this is true, may not as yet be 

 clearly shown in the present state of mining operations in this country. The fact that veins 

 wliose walls are strong and hard give a greater abundance of metallic matter than where they 

 are soft and yielding, is admitted ; and that those parts of the mine which are composed of 

 hard walls contain a larger and wider vein than other portions which are in an opposite con- 

 dition, is well known to all the experienced miners. Admitting the general facts as here 

 stated, it is not easy to offer a satisfactory reason for this state of things. In the Second Dis- 

 trict, there arc several mines in this rock, some of which have been wrought to the depth of 

 two hundred feet or more. This, it is true, is not to be compared to European mines ; but 

 it is sufficient to give us satisfactory conclusions as it regards the constancy of the mineral 

 matter when in distinct veins. The two principal minerals which have been obtained from 

 this rock, are lead and iron, botii of which occur in veins which have been explored to the 

 depth of two hundred feet. Without anticipating what I have to say in relation to these two 

 substances, in the proper place, I have only to remark, that very little change was found in 

 the quality of mineral matter at the depth here stated, from that at the surface : if there was 

 no increase, it is clear that the decrease has been so small that it has not been observed. 

 Even thin and unimportant veins have been pursued for some considerable distance, without 

 finding a diminution of ore. 



These remarks apply to those mines which are clearly in gneiss ; for to those which are 

 situated in rocks subordinate to this, as limestone, serpentine, etc. they will not be found to 

 hold good. Neither are they true of those mineral substances which are diffused or dissemi- 

 nated through it ; for those substances which are thus associated are always uncertain in their 

 extent, and in the amount of ore whicli they furnish. But veins whicii are distinct and well 

 defined appear to be always well filled in this rock, in the Northern District, and to carry tlie 

 mineral matter to as great a depth as has yet been explored, without material diminution or 

 the substitution of an inferior one. It is true that different portions of the vein are not equally 

 rich and productive, and are not equally wide ; but many portions become wider by a reces- 



