484 Ele VV IR ORIN TD Ts 
this greenstone is a feldspathic rock, and not a fourchite. How- 
ever, if we suppose that the pyroxene in the specimen analyzed 
by Ransome be an ordinary aluminous augite, and that all the 
magnesia of the rock is in the augite, a calculation shows that 
the rock contained about 80 per cent. of augite, so that in this 
specimen the feldspar must have existed in small amount. The 
specimens from the Angel Island fourchite area which I 
examined have the structure and composition of a holocrystalline 
basalt in which the augite shows an idiomorphic tendency, as it 
often does in modern doleritic basalts. The Angel Island green- 
stone may, therefore, be called in part a metabasalt, and this 
term should likewise be extended to the basaltic rocks at Pt. 
Bonita, inasmuch as in all cases the basalts have undergone 
extensive metamorphism. A comparison of the analyses of the 
spheroidal basalt at Pt. Bonita, with that of the fourchite at 
Angel Island, and of other greenstones from other portions of 
the Coast Ranges," brings out very clearly the similarity in com- 
position of these greenstones at widely separated localities. 
ANALYSES OF METABASALTS AND DIABASES FROM THE COAST 
RANGES. 
rpaeee Ill IV Mi 
P fo) it Q 
Rourcute aoe . Diabase, Diabase, Spheods 
Fourche Mt. nee! Pt. Bonita | Pt. Bonita Pt. Bonita 
Siltcasasr tierce see aot ener 42.03 46.98 45-59 46.28 49.45 
Allnummnlivaleays aes a cic ive soseverecieron Selene oale'.00 17.07 20.99 12.96 17.58 
WETNC ORNGCISs5 06a vb0 e000 08 7.55 1.85 2.49 4.67 3.41 
FSMAUIS) ORAGKESo Jaco upcosucaue 6.65 7.02 4.36 6.06 3.41 
Ash gaVEhr eeercicistiaee orenusa eeeoo oe 14.15 12.15 7.57 10.12 7.20 
Nialgilesiavaretn eens sone: 6.41 8.29 8.95 8.71 4.05 
IROtASS ai lgecer a aaa ae Aa as 97 Bee i 1.57 
Sodlagieyyc ee ccc, Somer rns 1.83 Anish || \) 4.89 3-75: 5.83 
IAIMIAN YS tesitst siecheteyee seateneye se sia Brackett | Ransome | Ransome | Ransome | Ransome 
and Noyes 
1. Fourchite from Fourche Mountain, Arkansas. (Ann. 
Rept.) Geol? Surv., “Arkansas, 1698, Voll. II, on “The Igneous 
Rocks of Arkansas,” by J. Francis Williams, p. 108.) This 
See table of analyses. 
