G. W. Hawes—Trap Rocks of the Connecticut Valley. 187 
These analyses show it to be dolerite, differing from the trap 
of West Rock in the proportion of its ingre 
- specimen from the Mesozoic sandstone region of New Jer- 
taken from a deep railroad cut in Jersey City, afforded the 
following results : 
JERSEY City. Sp. gr. = 2°96. 
1. 
i Mean. 
Silies ol fo ture 53°16 53°09 53°13 
Adumings ¢. 5. ic 13°87 13°62 13°74 
Ferrous oxide _.. 9°09 9°10 9°10 
Ferric oxide .__.. 1°01 1°14 1°08 
insane oxide °44 43 43 
LARS: cea ak 9°44 9°50 9°47 
Monee cease 8°56 8°59 8°58 
Coe Seo aed 2-28 2°32 2°30 
POUR aac cee 1°08 1°04 1°03 
jJgmtion...../.- = 80 91 Pie 
99°77 99°74 99°76 
Another specimen taken from a trap hill lying to the east- 
ward of New Haven, called East Rock, was also analyzed. But 
enough ie been given to show the uniform character of the 
unaltered rocks of this era; no two analyses differing from one 
another more than would those of samples which could be se- 
lected from the same dike. 
The principal mineral ingredients are pyroxene and labra- 
dorite, with a small amount of magnetite, and often, as Mr. 
Dana has detected by his ileneaetis examinations, a little 
chrysolite and apatite. The pyroxene can be recognized by its 
Cleavage. Spots are sometimes found in the rock ahers the 
crystals of pyroxene have considerable size, and often the pris- 
matic angle as well as the basal cleavage can be distinctly seen. 
From one piece it was possible to extract a sufficient number 
of crystalline fragments of apparent purity for an analysis. 
PYROXENE FROM WEST ROCK. 
SUCK. pi ad onbeae vis ayer ah « 50°71 
PTR i a 3°55 
FOrnQUS. OF500 5 oid Ga ces ons deen x 15°30 
nee ORMIG 0g. ees Sw cee 81 
wed eee: 13°35 
Mag aE sine agen 13°63 
Ign gue BEY re See ares pie ho ENB A et 1°17 
Alkalies and loss (by difference) .-.. 1°48 
100-00 
On comparing this analysis with those of the dolerites, it 
leaves little doubt but that the feldspar is labradorite, as the 
