286 PENTTI ESKOLA 



allow wollastonite to be formed,^ and quartz is generally found in 

 contact with calcite. 



Quartz limestone is the most widely distributed type in western 

 Massachusetts. Most of the Stockbridge limestone belongs to it 

 and, also, much of the Coles Brook limestone. Such were the 

 specimens from Goose Pond Creek and East Lee described above 

 (p. 272). They consist of dolomite and quartz, sometimes with 

 microcline. 



During the excursions we did not happen to meet with any 

 typical tremolite limestone, but it is apparent from Emerson's 

 descriptions that it is a common type, in the Stockbridge as well 

 as in the Coles Brook.^ 



Tremolite limestone is noted "south of Becket" (Emerson, 

 U.S. Geol. Surv., Mon. 2g, p. 27), and from Lee (U.S. Geol. Surv., 

 Bull, i^g, p. 84). Tremolite but no pyroxene in limestone is 

 mentioned in the "Mineral Lexicon of Eastern Berkshire Co." 

 (last-cited volume) from Windsor, Monterey, and the Cobble in 

 Tyringham. 



Through the courtesy of Mr. E. V. Shannon the writer was 

 able to study specimens from the collections of the United States 

 National Museum of tremolite limestone (Stockbridge) from Lee, 

 Massachusetts, and from Canaan, Connecticut, near the Massa- 

 chusetts line. The rock from both localities was found to consist 



' Cf. footnote i on p. 285. 



' It might be objected that it is not justifiable to regard the Stockbridge and the 

 Coles Brook limestones as equivalents in their metamorphic development. For, if 

 the former is Cambrian, while the latter, with the Becket gneiss intrusive in it, is 

 pre-Cambrian, the Stockbridge cannot have been influenced by the heat of this intru- 

 sion which undoubtedly has changed the Coles Brook limestone. Now the plain 

 fact is that the same three types of mineral paragenesis occur in both of them. The 

 Coles Brook limestone, when belonging to the quartz type, is exactly like the most 

 common type of Stockbridge limestone. The occurrence of tourmaline in the latter, 

 recorded above, points to the vicinity of magmas. Emerson knew this, and he assumed 

 that there may be post-Cambrian igneous masses not quite exposed on the present 

 land surface. If this is true, then the earlier and the later intrusions have taken place 

 during very similar physical conditions. It seems worth while, in future investigation 

 of the geology of western Massachusetts, to consider the possibility that the Becket 

 gneiss is of post-Cambrian origin, and the Coles Brook limestone only the margin of 

 the Stockbridge. In fact our observations at the eastern as well as at the western 

 contact of the Becket batholith seemed to indicate that this is the case. 



