104 A PEEIDOT1TE FROM MAINE. 



think, lead petrographers in general to regard it as a product only of 

 high temperature, and hence not to be looked for under such circum- 

 stances or conditions as the hornblendic and feldspathic enlargements 

 to which allusion has been made. The fact that the mineral reaches 

 out in slender, thread like prolongations into the curvilinear fractures 

 of the olivine shows beyond controversy that so much of the mineral 

 has formed subsequent to the fracturing of the olivine. That it was 

 not all so formed is shown by the well-defined curved borders abutting. 

 fairly against the olivine pseudomorphs. At present I can see no possi- 

 ble explanation of these structures other than to consider them as 

 secondary, if indeed not contemporaneous in origin with the serpen- 

 tinization of the olivine. 



Fully one-half the interstitial spaces of the olivine are now occupied 

 by a very light greenish chloride substance, almost colorless in the sec- 

 tion and without action on polarized light, so that between crossed 

 nicols the now serpentinized oliviues appear as if set in a black frame. 

 (See Fig. 1 of Plate \xxiv.) These areas are precisely similar to those 

 occupied by the augite, and the first suggestion that offers itself is that 

 the amorphous material is the ultimate product of the augitic alteration. 

 Indeed, in some cases it is possible to trace the fresh augite through 

 its various stages of alteration until a somewhat similar product is 

 reached. In other eases, however, the fresh augites abut fairly against 

 and even inclose areas of this amorphous material in such a manner as 

 to force one to the conclusion that it represents the original unindividual- 

 ized base. The olivine, which constituted originally fully two-thirds the 

 mass of the rock, has in nearly every case examined gone over into a 

 serpeiUiuous product. That the mineral was undoubtedly olivine is 

 shown by the outline of the serpentine pseudomorphs, as well as the 

 irregular net-work of curvilinear fracture lines along which the serpen- 

 tinization has proceeded. The process of change h;is gone on with the 

 separation of free iron oxides in the manner so well known as to need 

 no further notice here. 



Magnetite occurs in abundance both as original and as a secondary 

 constituent from the serpentiuized olivine. Chromic iron is also present 

 in beautiful minute octahedra with a brilliant luster. It is not in all 

 cases possible to distinguish between the two ores by the microscope, 

 and as both were attracted by the magnet the presence of chromium 

 was determined by testing the separated ores in the borax bead. Tests 

 faded to show even a trace of titanium. Traces of a plagioclase felds- 

 par, although indicated by the analysis, are scarcely discernable in the 

 section. In but a few instances nearly amorphous chloritic areas were 

 observed still showing scarcely recognizable cleavage lines and twin 

 stria-. 



Besides the mineral above named, the slides show occasional small 

 prisms of apatite and rarely clusters of long, colorless, parallel-lying 

 needles, tapering gradually toward one end, and with frequent trans- 



