186 G. W. Hawes—Trap Rocks of the Connecticut Valley. 
uniform character of the ejected material, and what were the 
changes which took place to alter it into its present varieties, 
and what were the causes of the same. 
The specimens of which analyses are here given have in 
general been taken from railroad cuts or working quarries, 
in order to avoid material which had been altered by sur- 
face action. 
1. DoLErire. 
Lying to the west of New Haven there is a long ridge of 
trap, ending in a high bluff which is called West Rock. The 
trap is very firm, and analyses show it to be dolerite, the typical 
rock of this region. 
West Rook. Sp. gr. = 3°03. 
I. IL Mean. 
ON ee ea a 51°80 51°76 51°78 
MINS Se ok 14°21 14°19 14°20 
Ferrous oxide __. 8°26 8:23 8°25 
Fer ie... SSS 3°62 3°59 
Manganous oxide 42 “45 44 
irG: ccs Sey 0°68 10°73 10°70 
Magnesia ._..... 63 7°64 7°63 
ee 2°15 2°13 2°14 
Poesh >. 2 Gg 38 "39 
Phosphoric noid <2. 14 14 “14 
Ignition .-...... "63 "64 63 
99°86 99°91 99°89 
Mean 
Bien cig 52°70 52°65 52°68 
Alumina .___-_.. 14°11 14°17 14°14 
Ferrous oxide... 9°78 9°80 9°79 
Ferric oxide _... 1°87 2°03 1°95 
Manganous oxide 45 “44 “44 
Sime efi 9°36 9°39 9°38 
Magnesia __.._-. 6°42 6°35 6°38 
Bi eek 2°54 2°57 2°56 
Sees "89 87 ‘87 
igwition. o. +, 1°61 1°58 1°60 
Shien Bie aes : 5 See 
Ae a ne ree I Oe ee OS ge oe Foye eee Heh Pree one te 
