170 WILLIAM J. MILLER 
envelopes olivine, the former has secondarily developed from the 
latter. The olivine cores are of very irregular shapes and_in all 
sizes. Where hypersthene forms the core it is probable that all of 
the original olivine has been altered to hypersthene. The common 
occurrence of hornblende rims around pyroxene strongly suggests 
the derivation of the former from the latter. Garnet is almost 
invariably in contact with feldspar, which suggests the partial for- 
mation, at least, of the garnet from the feldspar. 
CHEMICAL COMPOSITION, NORM, AND MODE 
Excellent exposures of what is regarded as very typical gabbro 
occur in the railroad cut 14 miles south of The Glen. This rock 
has been chemically analyzed for the writer by Professor E. W. 
Morley. The following table shows the chemical composition, 
norm, and mode, the last having been determined from thin- 
sections. 
TABLE II 
Chem. Comp. Norm Mode 
SiO eae Mian ae 46.40 Orthies cs (hee 6.67 Plagioclase..... 32.72 
INO Sete araidiootio 14.17 AU ess ee BD 8B Orthoclase..... Bayo 
INGO oo Goucoced 2.03 AMOI see aera 225 Hornblende.... 27.92 
HeOr ee Same 13.12 Nai Glee geataen .82 Hypersthene... 14.30 
Mig Oe te oeieyere 4.94 iDrrne ere tae eyeie 5-78 Biotite........ 7.09 
CaO ie cera 9.65 IES Alstom 3.02 ANUMIDs 5505 00° 3.20 
Na Oates 3.14 Rye Ne Med 24 Garnet aenee 4.30 
KOR eae ae 1.12 ADA amen fet ar 2.02 Ilmenite....... 4.17 
H,O-+ 02 DIOP ss a caee ASS Pyriteeeeeeere 2.08 
H,O— 25 IBNANAGS 64g gov} 8.02 Apatite ns acne 36 
PIO Reser ices 3.03 OlivaRGtache 9.32 
PLO Rees aa .80 H,O-+ZrO,....: .32 
CO i regaie vale. 15 
Min @ iis eeeenene 44 
SE Sueno cosiy a .14 Class IIT Order 5 Rang 3 Subrang 4 
Baie Pain its .18 Salfemane Gallare Camptonase Camptonose 
SLO eye eeu ee. .10 
1 ESR SES .O4 
ZIO set heceetaee .05 
Motal eer eee Oni 
Under the old qualitative system the rock is a hornblende 
norite, while according to the quantitative system it is a hornblende- 
camptonose. 
