HILL: GEOLOGY OF JAMAICA. Lis 
This material and the accompanying phenomena of the outcrop have 
heen described by Brown,’ as follows : — 
“The kinds of rock of which it is composed are amygdaloid and a 
Pasty-looking brown agglomerate, ‘The amygdaloid is composed of a 
hard blackish base or matrix containing kernels of carbonate of lime, 
and the agglomerate is made up of blocks of this amygdaloid embedded 
™ à reddish iron stained material, which is extremely siliceous. Down 
the slope from the top of the volcanic ridge to the valley the bare patches 
of brownish lava, with blocks of amygdaloid sticking in them, evidently 
indicate the direction of the old lava flows. Masses of rock jut out from 
the face of the hill, which have all the appearance of huge rubble walls 
“emented with lime; on examination they are found to consist of large 
blocks of lava intermingled with white limestone. In these the lime- 
Stone has become cherty.” 
Two hand specimens of this rock petrographically studied by Cross 
Vere determined by him as follows :— 
No. 143, — District of St. George. Low Layton. Basalt. (Plagio- 
clastic.) Fresh typical basalt, holocrystalline, vesicles filled with crys- 
talline calcite, No Globigerina. 
No, 141. — Low Layton. Dense reddish groundmass obscured by fer- 
"tic material and containing olivine (altered), plagioclase, and angite. 
icles partly filled with very distinct Globigerina. 
Since the date of Brown’s observations, the Jamaican Railway has tun- 
nelled through the base of the hill, but the only new data it contributes 
55 the fact that the igneous rocks are encountered 700 feet below the 
Summit of the hill, and shows the latter to be of the nature of a volcanic 
Neck rather than an entirely superficial lava flow. 
: It is also probably older than the Post-Pliocene to which Brown as- 
Signed it, Our reasons for the latter conclusions are as follows. The 
fact, that the débris of the basalt is intermingled with the flint bearing 
Whito limestone of Vicksburg age (supposed to be Miocene or later by the 
Amaican Geological Survey) does not necessarily prove the Post-Eocene 
a of the basalt. On the contrary, the presence of the characteristic 
Ssils and chalk of the Montpelier limestone in the scoriaceous cavities 
o the basalt clearly shows that this limestone was deposited contem- 
00 ; à 
I "neously with or after the basalt. The yellow calcareous marls de- 
Seribed 
i as lying almost horizontally upon portions of the voleano were 
ent : 
atively considered at the time of our examination to be the Buff 
1 P 1 
Jamaican Reports, p. 120. These rocks were also mentioned by De la Beche, 
a 
D, Cit, , pp. 185-187. 
VOL, XXXIV. : 
