64 NEW YORK STATE MUSEUM 



morainal deposit, the Waterman Hill drumlin, which ettectively 

 prevents any certainty in the matter. Xevertheless at the point 

 where there is greatest proximity, and where they would be most 

 likely to join, the sigmoid amphibolite strikes in the general direc- 

 tion of the eastern terminus of the Pyrites amphibolite. ^loreover, 

 the attitude of the granite gneiss and associated Grenville forma- 

 tions a mile to a mile and a half northeast of Waterman hill con- 

 finns this structure, and makes it appear that the northerly strike 

 of the amphibolite south of V\'aterman hill is not a mere local phe- 

 nomenon, but is part of a broader structural tendency of consider- 

 able areal importance. It is also very unlikely that two separate 

 amphibolite formations of such magnitude should both happen to 

 pinch out entirely at this particular point, or that they should be 

 entirely distinct petrologic units brought into this significant juxta- 

 position by some tectonic accident. The chief point which favors 

 their being regarded as separate rock units, and which indeed led to 

 their being mapped as such, is the total lack of injected granite in the 

 Pyrites amphibolite and the copious development of granitic lenses 

 and injection zones of all grades in the Pierrepont amphibolite. 

 Whether this petrologic consideration outweighs the structural and 

 areal features described above, must be left an open question, and 

 till more is known of the bedrock underlying the Potsdam sandstone 

 below the Waterman Hill drumlin, the amphibolite areas will have 

 to be considered separate. 



If. on the other hand, they should prove to be continuous, they 

 will furnish a most remarkable illustration of the complexity of 

 Precambrian folding. The formation enters the quadrangle near 

 the southwest comer and bowing in general northward follows a 

 meandering curve 25 miles long to the southeast corner 13 miles dis- 

 tant, having meanwhile described a distorted, almost recumbent 

 ]\I-shaped pitching fold, whose limbs and axial planes are parallel 

 to the average northeast trend of the formations in this part of the 

 Adirondacks. The possibility of such a structure as this anywhere 

 else on the northwest fiank of the Adirondacks should deter one 

 from a too hasty attempt at estimating the thickness of Grenville or 

 other material in this region, any part of which is apparently liable 

 to an almost indefinite amount of repetition through isoclinal fold- 

 ing of this character. In the drift-covered portion of the present 

 quadrangle, in spite of the restricted area and short distances in- 

 volved, the writer has felt the force of this uncertainty concemingj 



