120 NEW YORK STATE MUSEUM 



unknown. In a similar way large red garnets w^ere at one time 

 revealed in these same pits. 



In the Smith mine, how^ever, and from the Cook shaft which 

 taps the northern end of this ore body, some of the most interesting 

 pegmatite has been revealed. It consists of very coarse quartz and 

 feldspar, with which allanite in irregular crystals up to the size 

 of one's hand is richly disseminated. Rarely good terminations 

 can be obtained, but the mineral is so brittle that it can not be freed 

 from the matrix except by the exercise of great care [sec Ries, H. 

 Allanite Crystals from Mineville, Essex County, N. Y. N. Y, 

 Acad. Sci. Trans. 1898. 16:327-29]. The dump is chiefly the 

 product of early mining, although some pegmatite has come up in 

 carloads of recently excavated waste rock. 



These pegmatites and their associated minerals, some of them 

 at least unusual in this abundance, are strongly suggestive of 

 igneous phenomena and to the expiring stages of some intrusive 

 mass they would naturally be referred. If, as seems most rea- 

 sonable for Old Bed, "21 " and Barton hill, we connect them with 

 the ore, they must mark an attendant phase of its separation. Other- 

 wise they must have come from some separate intrusive mass at a 

 greater or less distance and one which it is not easy to identify. 

 The basic gabbros would suggest themselves. 



One can scarcely attribute the pegmatites to regional metamorphic 

 processes. 



Revision of local geology. The geologic map here given shows 

 somewhat different relations in the Barton liill area in regard to 

 the distribution of the gneisses and gabbro than were shown on 

 the map published by the writer in 1898. It also introduces the 

 syenite series as embracing the several gneisses called " 21," 

 " Orchard " and '' Barton." The syenite series has been described 

 on earlier pages, with analyses and calculations of mineralogy, 

 which will serve to make the significance clear. As stated in the 

 general discussion of the syenites, the ores are regarded as basic 

 segregations in an eruptive mass of this character. 



Origin of the ore. In all our work hitherto the gabbros have 

 been believed to be the latest intrusive of the larger masses. That 

 they penetrate the anorthosites as dikes is certainly true, because 

 among others the great dike at Avalanche lake — at the source of 

 the Hudson — shows these relations. As against the Grenville 

 series they are also believed to be intrusive, although decisive con- 

 tacts are not so clearly shown as with the anorthosites. But since 

 the- anorthosites are known to be later than the Grenville and older 



