THE TERRESTRIAL PERIDOTITES. — SERPENTINE. 157 



be read as clearly as in those rocks whicli arc only partially altered. The picture was 

 there ; the polarized light served as the developer only. Figures 5 and G, Plate Y., show 

 the structure of this rock. 



1404, from the same locality as the preceding, is a greenish- and brownish-black rock, 

 with lighter greeuish spots, and coated with light greenish serpentine on " slickeuside " 

 surfaces. 



Section : a yellowisli and gray mass spriidcled with black spots of iron ore and in 

 places traversed by a reticulated network of the same. It is composed principally of 

 serpentine containing crystals and granules of iron ore, besides being traversed in much 

 of its mass by the network of the same. It is also stained brownisli-yellow by oxide of 

 iron. In portions of the section are grayish spots, which sometimes show in their 

 interior greenish grains. These interior grains are remnants of the original olivine, 

 while the gray portions are formed of the serpentinized olivine traversed by numerous 

 fissures filled with innumerable dust-like granules. The iron ore in a few points is feebly 

 translucent, and iu part shows no metallic reflection, but it is traversed by bands that do 

 show the metallic lustre. Therefore it is probably a mixture of chromite and magnetite, 

 which appear to be commonly associated in the majority of serpentines. The general 

 structure is represented in figure 5, Plate IV. 



1567 is a rock that in the hand specimens appears to be the same as No. 1404, but no 

 sections of it have been prepared. 



1563, from the same locality,* is very similar to No. 1403, but is more altered and 

 weathered. It contains chromite and talc. It has a yellowish-green grounduiass of ser- 

 pentine traversed by innumerable reticulated veinlets of a dark green to black serpentine. 

 These veinlets give a structure to the rock that might be taken by some for stratification. 



Section : a gi-ayish-green mass formed of translucent, feebly polarizing, grayish, finely 

 granular serpentinous material, traversed by a network of innumerable veins of clear, 

 more or less brilliantly polarizing serpentine. Much chromite occurs in irregular 

 pronged masses, grains, and heaps of grains, principally arranged along the serpentine 

 veins. While some may be original or else picotite altered m situ, the chief portion 

 appears to be of secondary origin in the serpentine. 



1564, from the same locality, is a dark-greenish rock filled with talc scales and 

 weathering to a yellowish rust-like product, with the talc masses protruding from the 

 surface. Tiiis talc forms crystalline masses similar to those formed by chlorite. 



The section is an irregular mixture of pale yellowish serpentine and grayish-wliite 

 talc with iron ore. The ore is principally associated with the talc, forming bands along 

 the cleavage planes. The talc plates are partly isotropic and partly feebly polarizing, 

 and are colorless or gi'ay. The structure and relations of the serpentine and talc are such 

 as to indicate that the serpentine has replaced the olivine, and the talc the pyroxene 

 minerals. ^ 



Zohlits, Saxony. 



5001. A mixed reticulated greenish and brownish-red rock, containing roundish 

 reddish-black to black spots. 



Section : greenish- and brownish-red with grayish-black spots. The principal portion 

 of the section is serpentine. This shows the reticulated structure in common and 

 polarized light, frequently having between the colorless meshes greenish patches repre- 



* All the High Bridge, New Jersey, serpentines were the gift of Mr. S. II. Deau. 



