TONALITE. 335 



It is put as an "exotic Montalban granite" on the "centennial map" of 

 W. 0. Crosby/ because it is micaceous as well as liornbleudic and because 

 it contains a center of true g-ranite (according to President Jlitclicock's map 

 of 1844) in the southwest corner of Belchertown — a groundless argument, 

 since the granite in question is simply a great pegmatite dike which cuts 

 the tonalite. 



DISTRIBUTION. 



Uii the west side of the river the rock commences in Whately, a short 

 distance southwest of the \'illage, where it is seen in contact with the 

 Leyden argillite, producing a marked contact metamorphism (p. 205), and 

 runs south in a long, bare ridge ("The Rocks"), like a great dike, into 

 Northampton, where it ends in Elizabeth Rock. It is (J miles long and 2 

 miles wide. East, west, and south broad areas of sands and sandstones 

 separate it from its neighbors. To the west of its south end it grades 

 into a great area of biotite-gTanite identical with itself except in the absence 

 of hornblende. 



On the east side of the river a great squarish mass occupies the south- 

 west portion of Belchertown, extending into Granby and Ludlow, its con- 

 tacts, unfortunately, greatly obscured by the heavy post-Glacial sands. It 

 is a great batholite and in many places strong contact metamorphism can 

 be observed at its borders and in broad sheets of schists that float out in 

 the center of the great mass. (See p. 243.) 



North from the northwest corner of the area of tonalite across Belcher- 

 town and Pelham, and so on north in the foothills, is a line of outcrops 

 of much crushed rock which seem at times like amphibolite shot through 

 by many small aplite veins and at times like the tonalite. The Slniys flint 

 is a peculiar facies of this rock which resembles a petrosilex. As it runs 

 along the western border of Mount Hygeia it is quite gneissoid, but appears 

 in Leverett in typical development as a beautiful dark-green granitoid rock 

 shot through with epidote veins. Also, going north from the northeast cor- 

 ner of the Belchertown mass along the corresponding eastern foothills of 

 the next valley to the east, across Prescott and New Salem, a similar line 

 of tonalite outcrops occurs, ending with the great lilock of diorite on the 

 north line of Prescott. These are both lines of strong faulting and crushing. 



' Report on a Geological Map of Massachusetts, p. 



