160 PERIDOTITE. 



quite ii rectangular grating, ami much talc is present in curved and bent fibrous masses. 

 The general structure of this section is shown in figure 2, Plate VII. 



1081, also from ]\Ir. S. H. Dean, was obtained by him from the bed of the West- 

 field Kiver in Eussell, Massachusetts. This is a leek-green serpentine, containing 

 grains of chromite and closely resembling that from Chester and Texas, Pennsylvania. 

 No section. 



Ljinnficld, MassacJmselts. 



1087. Section : pale yellowish-green, mottled with spots of clear grayish-white and 

 with dust and grains of iron ore. In common light under the microscope, the greenish 

 portion shows the dirty green spots commonly seen, formed from the alteration of the 

 unfissured central portion of the olivine grains. In polarized light it shows the common 

 reticulated meshwork of most alteration serpentine. The clear grayish-white portions are 

 formed of interlacing and divergent fibres and plates, optically orthorhombic, and polar- 

 izing with clear, beautiful tints, varying from yellowish-white to yellow and red. The 

 iron ore is crystalline granular, opaque, has but little lustre, and resembles chromite. 

 The forms of the larger grains resemble those of picotite wdien only partially altered. 

 The general structure is shown in Plate VI. figure 2. 



The hand specimen is a dark grayish-green compact rock, mottled with black iron ore 

 and talc scales. This specimen was kindly presented to the collection l)y Professor N. S. 

 Shaler. Later the locality has been visited by Professor J. D. Wliitney and myself, and 

 other specimens answering in general characters to the above were obtained. While this 

 serpentine is much jointed, no evidence of stratification was seen, and it was apparent 

 that the approximately parallel jointing had been taken for stratification by previous 

 observers. No contacts with the adjacent rock could be found. In a pit near the quarry 

 the rock is a mottled dark grayish-black one, which in thin splinters is dark green. 



A serpentine of much finer quality and of a dark green color, was found outcropping 

 by the side of the road to the northwest. A dark green much broken and fissured ser- 

 pentine outcrops opposite C. W. Hersey's blacksmith's sliop, in Peabody, on the road 

 near the line between that town and Lynnfield. While no definite field evidence regard- 

 ing its origin could be obtained, the general appearance of the outcrops was that of an 

 eruptive mass metamorphosed, nothing being observed that indicated either chemical or 

 mechanical sedimentation.* 



The Lynnfield serpentine shows when tested the presence of chromium, and the rock 

 powder is magnetic. 



From the road between La Vega and Jarahacoa, at the first crossing of the River Joa 

 going from the former town, Province of La Vega, San Domingo. 



141 G. This is a much altered foliated rock, composed essentially of light greenish- 

 white and yellowish darker green serpentine. The foliated structure appears to be 

 entirely due to the alteration and pressure to which the rock lias been subjected. No 

 section was made of this rock. Collected by W. M. Gabb. 



* See also Crosby, Oecas. Papers, Bost. See. Nat. Hist., ISSO, iii. 115 ; Hitchcock, Fiual Report, 

 Gool. Mass., 1S41, ]). 159. 



