TONALITE. 333 



'I'he inclusions may have been rounded by slow solution in the melted 

 mag-ma, this solution attacking corners and. edges most rapidly. That the 

 inclosing rock is an igneous rock is certain from its microscopical character 

 and its contact ettect. That the pebble-like masses ai-e true foreign "inclu- 

 sions" does seem ])robal)le from their lithological variety and difference 

 from the inclosing rock. They closely resemble pebbles rouiuhnl l)y water, 

 but so many cases of such inclusions rounded by melting (as granite in 

 lamprophyre and quartz in various magmas) have been descril)ed that this 

 may be the explanation.' 



I am, however, more inclined to consider them secretions in tlic iikiss 

 of the rock itself, as they seem to belong wholly to two types which occur 

 commonly in this way. The one is a coarse, black hornlilcnde-biotite 

 aggregate, such as is often seen in small masses anywhere in the rock. 

 Slides of this showed it to agree with tliese concretionary masses, and not 

 with any amphibolite known as an independent rock in the region. The 

 other is a tine-grained granite (jr eurite, like that so common in the veins 

 that cut the rock abundantly. Both these rocks seem to have separated 

 from the magma, to have been accumulated here in unusual amount, and 

 to have been rounded by resorption according to the methods discussed 

 in the articles cited above. 



The locality where these forms are found is at the upj)er dam at West 

 Brook, on the north line of Hatfield. 



A third most interesting variety of the syenite is described as follows : 



Augitic syenite. — The presence of hornblende in this variety and the absence of 

 luica have led me to call it augitic .syenite rather than augitic j;raiiite, although in 

 position it is associated with granite. There are two varieties. The lirst is com- 

 posed of black hornblende, greenish augite, and yellowish feldspar, all the ingre- 

 dients except the feldspar exhibiting a very distinct and lively crystallization. This 

 variety occurs in the northern part of Belchertown. The other variety, which I 

 have found only in bowlders in Amherst, consists of augite and feldspar, the former 

 being so arranged in the latter as to present the appearance of letters.- 



He insists, further, on the low level occupied by the syenite in the 

 valley and upon its columnar structure, and describes in cousiderable 

 detail the segregated veins which occur so aliundantly. He presents a 



' See, for .several citations, R. Pohlman, Einschliisse von Granit in Lamprophyr : Neues Jahrbucli 

 fiir Mineral, etc., 1888, II, p. 87, and note on page 92. 



- This 18 a contact modification of the amphibolite bordering the granite and is described on 

 p. 243. 



