276 SMYTH — ROCKS OF NORTHWESTERN ADIRONDACK REGION. 



again. It would be impossible to examine these outcrops without being 

 convinced of the irruptive nature of the contact. 



If any further structural evidence were needed to substantiate this 

 view, it would be afforded by the presence of included masses of. the 

 older rocks in the intrusive. These are shown on a small scale near 

 Natural Bridge, but a more instructive example occurs about a mile 



southeast of Harrisville. Here 

 **■"'■■ ' '" ;.<r^^?}^;>.-v_ ^ • the gabbro contains abundant 



inclusions of fine grained, lam- 

 inated gneiss, such as occurs 

 interbedded with the lime- 

 stone. These inclusions vary 

 from a few inches to several 

 yards in diameter. The lami- 

 nation in the different blocks 

 has different directions. The 



Figure b.- Inclusions of Gneiss in Gabbro. outline is USUally rather irrcg- 



The drawing is made from photograph and field sketch -, /I +"K K /^ "K 



procured one mile northeast of Harrisville. ^^^^ ^^"^^ ^'^^ DOUnQary be- 



tween the inclusion and the 

 gabbro is very sharp, with no trace of gradation between them (see 

 figure 5). Sometimes the gabbro shows a banding near an inclusion and 

 parallel to the side of the latter. There can hardly be a doubt that this 

 is an original structure caused by the flowing of the molten magma 

 around the solid inclusion (see 

 figure 6). These facts clearly 

 prove that the blocks of fine 

 rock are inclusions and not of 

 the nature of segregations. As 

 they correspond in character to 

 the gneisses of the limestone 

 series, they furnish another proof 

 of the intrusive character of the 

 gabbro. ■ 



Less COnt^lusive, but of a con- The exposure, which is one mile southeast of Har- 



firmatory nature, is the fact that "^^^^^ '' ^T'^'^^t ^y gravel and the drawing is from 

 •^ a photograph and field sketch. 



at varying distances north of the 



main belt of gabbro there are numerous bosses cutting the limestone, 

 which seem to bear an important relation to the former rock. These 

 are generally quite small, but sometimes attain considerable dimensions. 

 The rock of these bosses is quite different from the ordinary gabbro 

 but closely resembles certain phases of the latter yet to be described. 



Figure i 



-Banding of Gabbro parallel to Side of Gabbro 

 Inclusion. 



