NEW YORK ACADEMY OF SCIENCES 581 



Through this depression the Peterskill probably flowed, while 

 its own valley and Coxing Clove were dammed by the front 

 of the ice sheet, and cut then the Paltz Gap in the crest of the 

 first anticline, 200 feet deep, through which the road to New 

 Paltz now runs. 



The basin of Lake Minnewaska is vertically walled except 

 at the southwest end. The cliffs are highest under Cliff House, 

 where they stand 160 feet above the surface of the lake and 

 65 feet below it. The grit is probably about 230 feet thick 

 here. The walls are pierced by four crevasses, now filled with 

 drift, — the remains of two fissures crossing each other at the 

 deepest point in the lake, which is there 74 feet deep. There 

 is no drift in the lake basin, not even under the south-facing 

 cliffs, although the fissure running S. 25 W. is filled, and the 

 transverse breach is blocked to 150 feet above the lake. The 

 glaciation is here S. io° W. The cause of the absence of drift 

 is not clear; elsewhere the cliffs are heavily skirted. 

 . Lake Awosting lies along a vertical fault plane, drift -filled 

 at both ends. The fault has not been studied. The north 

 wall of the Palmaghat is a vertical fault of 200 feet throw. 

 Both these faults seem to be derived from the overthrown 

 anticline of the Coxingkill escarpment. Mr. Barton is in 

 error in declaring the absence of extended faults. 



Dr. Julien, after a brief review of the life of Dr. Archibald 

 Bruce of New York City, the discoverer of brucite, discussed 

 the fact of the wide distribution of the mineral, both in lime- 

 stone and serpentinoids, either in its unchanged condition, or 

 in the form of its derivatives, especially magnesite and hydro- 

 magnesite, as maintained by Volger in 1855. 



The following are its most marked characteristics for recogni- 

 tion as a rock-constituent: 



1. In addition to the known basal cleavage, two other 

 systems may be distinguished on plates or folia: that of the 

 hexagonal prism, often becoming rhombohedral, intersecting 

 at 6o° or 120 ; and that of the hexagonal pyramid, intersecting 

 at 90 . 



2. Nemalitic structure or fibration, commonly occurring 

 in brucite, within serpentinoids subjected to dynamic stresses. 



