THE EASTEIIN AREA. 415 



foriiily tilt) same that there is every reason to beUeve that the detached 

 exj)osures are parts of" a continuous belt. 



The alterations have extended so far in places as to make the rock 

 a poi-jihyrite. If any of the rocks have had a glassy background, it has- 

 now wholly devitrified, and while it is at times very fine grained, the fresher 

 parts are always holocrystalline. The structure of tins background, in 

 rocks fresh enoug'h to determine this point, is hypidiomorphically granular. 

 The original minerals were menaccanite, plagioclase, and augite, this being 

 the order of crystallization. The secondary ones are kaoliuite, chlorite, epi- 

 dote, leucoxene, and smaragdite. The only mineral which appears in two 

 generations is the plagioclase. It is always greatly altered and no separa- 

 tion of it was attemjjted, but as indicated by its double angle, according to 

 Pumpelly's method, it is rather acidic, the angles determined being so low 

 as to indicate a feldspar not more basic in any case than labradorite. The 

 augite is occasionally found in unaltered, or little altered individuals, l)ut in 

 general it has very largely decomposed, while in several sections its decom- 

 position is complete. The change in the feldspars and augite has resulted 

 in the formation of the same set of minerals. One of the most abundant of 

 these, if not the most abundant, is smaragdite. It is found in small ])articles 

 and well defined blades, which penetrate the rock in every direction and 

 thus cut the feldspar tlu-ough and through. Chlorite is also an abundant 

 secondary product, and in it has developed a large quantity of epidote. 

 As a result of these changes in the augite and feldspar, the smaragdite, chlo- 

 rite, and epidote are the three most plentiful minerals of the rock. The 

 menaccanite is always altered to a greater or less degree to leucoxene, and 

 frequently gives the characteristic gi'ate-like appearance. 



In original minerals contained and in secondary products, these augite- 

 porpliyrites are almost precisely like the diabases of the first division. The 

 similarity is so remarkable as to make it jjrobable that the rocks of the two 

 divisions are or once were connected. This likeness is still further reenforced 

 by the correspondence of the double angles of the feldspars, as measured 

 by Pumpelly's method. 



The area in Sees. 13, 24, 14, and 15, T. 47 N., B. 44 W., MicJiirjan.— 

 The greenstones here included, unlike those of the twt) previous areas, are 



