PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 477 



Porphyryte. Trachyte.] 



No. 659. PORPHYRYTE. (Diabase.) 



"This rock appears to be in place, but can be seen only in the form of numerous loose pieces. It has the 

 appearance of constituting the top portion of the ridge (No. 658). * * This ridge runs east and west nearly, 

 on the north side of the trail, and rises about two hundred feet." This specimen is evidently from a trail on the 

 south line of sec. 16, T. 63-2 E., and east of Nos. 657 and 658. 



Ref. Annual Report, x, pages 69, 70. 



Meg. The rock is markedly porphyritic, with numerous white feldspar crystals. 

 The groundmass is of quite fine grain, dark gray in color, and consists of feldspar 

 and a black material. Some of the feldspar, both the porphyritic and that in the 

 groundmass, has a pinkish shade. 



Mir. The section shows porphyritic feldspars, usually lacking in crystal outline, 

 in a groundmass consisting of smaller lath-shaped feldspars, augite, magnetite and 

 alteration products. Almost all the feldspars are highly altered, gray and almost 

 opaque, sometimes showing epidote. The alteration products of the groundmass are 

 a green material (mostly chlorite), quartz, apparently feldspar much reddened, 

 magnetite and hematite. It seems probable that the alteration products of the 

 groundmass represent in part something besides augite, but just what, it is impos- 

 sible to say. Notwithstanding the highly altered nature of the rock there is still 

 considerable augite remaining. 



One section examined. 



Aye. Cabotian or Manitou. u. s. o. 



No. 660. PORPHYRYTE. (Diabase.) 



From the trail at the crossing of the line between ranges 2 and 3 east. Evidently at the extreme southeast 

 corner of sec. 13, T. 63-2 E. 



Ref. Annual Report, x, page 70. 



Meg. Macroscopically this rock is very similar to No. 659. 



Mir. This section resembles that of No. 659, except for the facts that the 

 feldspars of the groundmass are not so markedly lath-shaped and that the augite has 

 entirely disappeared. 



One section examined. 



Age. Cabotian or Manitou. u. s. o. 



No. 661. TRACHYTE (?) 



"One mile east of the town line (S. E. corner of sec. 13, T. 63-3 E.) is a reddish crystalline rock in place, 

 and this continues east two miles from the town line." 



Ref. Annual Report, x, page 70. ^ 



Meg. A reddish-brown rock, consisting of numerous small, red, porphyritic and 

 sub-porphyritic feldspars and a darker grouudmass. 



Mic. Porphyritic feldspars are seen in a groundmass of feldspar, quartz, 

 yellowish and greenish alteration products (among which are chlorite and epidote), 



