354 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



GEI«fERAL, SECTIOK OF TRIASSIC ROCKS. 



The Triassic rocks have been divided by the author in an earlier pub- 

 lication^ as follows: 



1. The Sugar Loaf arkose ; or the sandstone and conglomerate made 

 up of the debris of granite. 



2. The Mount Toby conglomerate ; or the coarse conglomerate made 

 up of large schist and quartzite pebbles. 



These two numbers are, speaking generally, the west and east shore 

 deposits. 



3. The Longmeadow brownstone ; or the red sandstone generally 

 marked by so-called fucoidal forms, which are probably concretions. 



4. The Chicopee shale ; or the calcareous red shale. 

 These two are the offshore and central beds of the series. 



5. The Granby tuff; or the diabase-tuff. 



6. The Holyoke and Deerfield diabase beds. 



7. The Black rock volcanic necks and the posterior diabase beds. 



The last three distinctions cover the fragmeutal, interbedded, and intru- 

 sive occurrences of the diabase, respectively ; excejjt that the posterior sheet 

 is ^ilaced with the injected necks, with one of which it is directly connected. 



THE SUGAR LOAF ARKOSE OR THE FELDSPATHIC SANDSTONE AND 

 CONGLOMERATE. 



This most persistent and abundant rock is a coarse, buff" arkose made 

 up largely of the slightly rounded and slightly weathered de'bris of a 

 muscovitic granite. The average grain is about an eighth to a third of an 

 inch, so that in a region of fine-grained rocks it would be called a conglom- 

 erate. It is slightly cemented by iron. It grades in one direction into 

 a medium-grained, buff, micaceous sandstone, more commonly through 

 coarse, pebbly arkose into a coarse conglomerate, in which the mass of the 

 rock is the same coarse, unworn granitic debris and the larger constituents 

 are large rounded pebbles — of granite when the rocks of the adjacent shore 

 ai-e granite. It is at times whitened over broad areas by the removal of 

 the iron cement by organic agencies and the complete kaolinization of its 

 feldspars to great depths. The red rock is first spotted with green from 

 the reduction of the iron oxide, and then whitens as the protoxide salt is 

 removed by solution. 



' On the Triassic in Massachusetts: Bull. Geol. Soc. America, Vol II, 1891, p. 451. 



