18 92. J NEW YORK ACADEMY OF SCIENCES. 127 



it. The rarity of these varieties is the warrant for the mention of 

 a boulder whose home is unknown, but which it is to be hoped may 

 be traced. The rock is formed by a dense grayisli-blaek ground- 

 mass, through which are thickly set great crystals of black horn- 

 blende and augite up to an inch or more in length, and at least half 

 as much in width. In thin section the ground-mass proves to be 

 glass, which is filled with minute colorless augites, about 0.1 mm. 

 and less in breadth, and several times as long. The large horn- 

 blendes are golden-brown, parallel to c and b, and faint yellow, 

 parallel to a. They fuse easily before the blowpipe with a strong 

 sodium flame. The cleavage angle, as kindly determined by Mr. 

 A. S. Eakle at the writer's request on a No. II Fuess Goniometer, 

 is 123° 55', and the signals were good. This would indicate 

 arfvedsonite, the soda amphibole, and the cleavage angle is the 

 same as that originally given by Brooke. There is also a cleavage 

 parallel to the plane of symmetry, but it is less perfect. In the 

 rock the crystals are bounded by the prism and this pinacoid. They 

 are also faintly zonal, the border being a darker brown. The 

 augite is eight-sided and almost colorless. There are some very 

 doubtful olivine remains. Of all the rocks described, the fourchite 

 which occurs with the elaeolite-syenite near Little Rock, Ark., is 

 nearest to this. The source of the boulder is probably in the crystal- 

 line Archaean rocks to the northeast, and it has probably come from 

 the Adirondack heights. The nearest exposure of these is distant 

 a hundred miles at least, but of their petrographic character we 

 know only in the most general way. It is also to be noted that 

 peridotite dikes have been recorded in the interval, at Syracuse,' 

 Manheim Bridge,^ and south of Aurora at Ithaca.' Some undis- 

 covered dike may have yielded the boulder. Professor Freley also 

 gave the writer a piece of a small boulder that is a most excellent 

 syenite. It indicates this rather unusual rock as existing in the 

 northern crystallines, and increases the interest which should be 

 felt in the study of the western Adirondacks. 



II. 



Xotes on Several Bocks Collected by E. E. Olcott, E.M., near Gold 

 Hill, Tooele Co., Utah. A series of rocks has lately been placed 

 in the hands of the writer which was collected by Mr. Olcott on 

 the western border of Utah, in the American Desert or on its con- 

 fines. They are of sufficient interest in one or two instances to de- 

 serve mention. S. F. Emmons, of the 40th Parallel Survey, has 

 recorded some notes of this region as it lay within his explorations 



1 G. H. Williams, The Serpentine (Peridotite) occurring in the Onondaga 

 Salt Group at Syracuse, N. Y. A. J. S., Aug. 1887, p. 137. 



2 C. H. Smytii, Jr., A Third Occurrence of Peridotite in Central New York ; 

 id. April, 1892, p. 322. 



3 J. F. Kemp, Peridotite in the Portage Sandstones near Ithaca, N. Y. ; id. 

 Nov. 1891, p. 410. 



