Sia AAT soil Neaeilin as Dip no a 
ee 
H. Hennessy on the Interior of the Earth. 461 
in the Eocene Dinoceras and Coryphodon, in the Miocene 
Brontotherium, and in the Pliocene Mastodon. But the 
May examine. The tendene ty ia just as plainly marked as that 
toward increase in cranial capacity or toward compactness and 
abbreviation of the anterior organs,—indeed it is undoubtedly 
correlated with the shortening and compacting of the jaws. 
nd it is probable that the ‘degree of development of any 
mammal, as the horse or pig, can be just as ania and relia- 
bly measured by the relative size of its molars y the size 
of its brain-case or by the presence or absence of ‘eprath bones 
of manus or pes. Casual statements to the effect that the rela- 
tive size of. the posterior molar varies inversely as the volume 
of the brain have indeed been met with, but no critical we 
cussion of the true significance of such relations; and the 
practical bearing on the work of the determination of perce 
American crania seems to have been wholly overlooked, as it 
certainly was in the discussion of yesterday. 
Planters’ Hotel, St. Louis, Aug. 23, 1878. 
Art. LIV.—On the Limits of Hypotheses gs ming the Properties 
of the ig, composing the laterior of the Harth; by HENRY 
Hennessy, F.R.S, Professor of Ap lied Riot in the 
Royal pale of Science for Ireland. 
1. From direct observation we are able to obtain only a very 
bebderdts knowledge of the materials existing below the solid 
crust of the earth. The depth te which we can penetrate by 
mining and boring operations into this crust is comparatively 
insignificant ; and these operations give us little knowledge of 
— earth’s interior in comparison with what is afforded by the 
rings of voleanoes. Two hundred active volcanoes are 
to still exist, while geologists have established that many 
Ecos of such deep apertures in the earth’s crust have 
existed during remote epochs of its physical history. The 
source or sources of supply for all these voleanoes ha ve poared 
out a predominating mass of matter in a state of liquidity from 
fusion. Evidence is thus furnished that matter in a state of 
fluidity exists very widely distributed through the earth. The 
1878. Read before the Mathematical and Sintoad 
cal jersiage dogma a regret for the Advancement of Science, Dublin, 
16. 
