188 G. W. Hawes—Trap Rocks of the Connecticut Valley. 
low percentage of silica and the presence of so much lime 
roves. The presence in one case of a feldspar with even a 
lower percentage of silica (see beyond) renders it improbable 
that the chief feldspar constituent has a higher percentage than 
labradorite. Moreover, in the analyses, making llowance 
for the magnetite, the oxygen ratio of the bases and silica is 
even less than one to two, which would not be the case if the 
feldspar were oligoclase. 
The magnetite, which is always present, is quite variable in 
amount. There is much more in the trap of West Rock than 
earthy debris reaches to the top of the ridge. A determination 
of the iron in this rock gave 
. I. 
ce ee be Bee 8°55 
Ce ae 5°30 5°35 
13°82 13°90 
A few feet distant, however, the rock becomes as firm and 
undecomposed as usual, showing that the gathering of the mag- 
netite was of no great extent. Often octahedral crystals of 
magnetite can be seen in the rock with the unaided eye. 
The analysis of the pyroxene shows it to be ordinary augite 
a 
nesia does not enter into the composition of the feldspar, the 
rier apd Re 2 ie a 
