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agreement with the circumstance that the agpaitic type is some- 
times represented among dyke rocks (certain tinguaites) even 
in petrographical provinces where no abyssal agpaites have been 
found. 
SPECIFIC GRAVITY OF THE ABYSSAL ROCKS 
OF ILIMAUSAK. 
While the specific gravity of an abyssal rock is a quantity 
of very little interest from the standpoint of the laccolitic theory 
of intrusion, the theory of batholitic invasion of subsidence of 
roof blocks demands that it be given considerable importance. 
Though we are not able to calculate the original specific 
gravity of the magma from the observed specific gravity of 
the rock, the latter quantity will in most cases give an ap- 
proximate idea of the relative specific gravities of different mag- 
mas. The peculiar stratification of one part of the flimausak 
batholite seems to show that in this peculiar case differences 
of specific gravity have not been without importance in the 
arrangement of its rocks. For these reasons the specific gravi- 
ties of the abyssal rocks of Ilimausak have been grouped to- 
gether in the following table. The determinations were made at 
about 20° C. 
As most of the rocks are conspicuously miarolitic Dr. 
STEENSTRUP suggested that it might be of interest to examine, 
not only the specific gravities of the rocks in a powdered con- 
dition, but also in large unbroken specimens. Thanks to his 
great kindness I am able to utilize the results which he ob- 
tained by weighing whole specimens, and subsequently deter- 
mining their volumes with a mercury volumenometer. The 
specimens used for these determinations weighed from 500 to 
1000 grams. The table shows that the porosity varies very 
