32 WILLIAM J. MILLER 



in many cases, practically pure silexite and ordinary pegmatite, 

 the one grading into the other, occur in the same inclusion or dike. 

 Just south of the southern summit of Alder Brook Mountains the 

 large bare ledges contain many pegmatite and silexite masses 

 which exhibit the features just described, the pegmatite and silexite 

 there often grading into each other. Some of these cut the granite 

 very irregularly in true dike form without very sharp contacts. 

 Phenomena like those above described have been observed in many 

 parts of the Lyon Mountain quadrangle. 



Figure 2 shows two larger masses of nearly pure silica (silexite) 

 with their long axes parallel to the fluxion structure of the inclos- 

 ing granite, with very distinct magmatic flow-structure foliation 

 curved about them, and with sharp contacts against the granite. 



A more exceptional case is shown by Fig. 3. The larger mass 

 of silexite is exceedingly irregular in shape, and it locally contains 

 considerable feldspar. Both inclusions seem to lie almost at right 

 angles to the foliation of the granite, though it is quite possible 

 that this ground-plan sketch does not actually represent the 

 position of the whole original larger mass of silexite from which 

 the inclusions were derived in the granite. Fluxion structure is 

 locally distinctly curved on one side of the smaller fragment of 

 silexite, and also between it and the larger fragment. 



Figure 4 shows a very interesting silexite dike unusually thick 

 at one end and with five clearly defined dikelike branches cutting 

 the granite at the other end. The silexite contains not over 10 

 per cent of feldspar scattered through it in tiny masses. Contacts 

 against the granite are only fairly sharp, and the foliation of the 

 granite nowhere curves around the silexite. This is quite certainly 

 a true dike of silexite, and it was formed later than the silexite of 

 Figs. 1,2, and 3, so it was not pulled apart by the granite magma 

 which had already nearly or quite consolidated. 



A small lens of silexite occurs as a distinct inclusion with sharp 

 contacts in one of the later pegmatites (see below) on the low 

 ridge one mile east-northeast of Goldsmith. 



A mass of nearly pure silica (silexite) which demonstrably 

 formed well before the solidification of the medium-grained granite 

 which contains it occurs on the ridge one mile northeast of the 



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