ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixix 
Igneous rocks underlie the red conglomerate above-mentioned, and 
vesicular cavities in them not only contain the siliceous deposits, but 
also, as is not uncommon in such rocks, zeolites, carbonate of lime, 
and other substances. ‘The base of the rock is compact, somewhat 
porphyritic, of a dark brown or chocolate colour, and when so 
weathered that the contents of the numerous small cavities have been 
decomposed, has the appearance of a vesicular trap rock. At a di- 
stance there is a faint appearance of stratification parallel to the over- 
lying conglomerate. Proceeding westward from the town of Ober- 
stein, the same amygdaloidal rocks continue, in places more porphy- 
ritic, nodules of small agates and chalcedony appearing sometimes to 
run in lines. 
These rocks are underlaid by others of a more compact character, 
succeeded in their turn by a highly crystalline greenstone. It is at 
Idal that the principal agate quarries are worked. Two varieties of 
trappean rock, having the appearance of a slight dip to the H.S.E., 
alternate with each other, one much softer than the other, and of a 
more amygdaloidal character. It contains numerous nodules, varying 
from an inch to a foot in length. Remarking that these nodules are 
lengthened out in the plane of the bed, Mr. Hamilton observes that 
this form may be due to pressure on the cavities while still in a vis- 
cous state, a point of much interest, as also indicating a movement 
of the mass in the direction of the lengthened cavities, such as may be 
observed elsewhere in rocks of this class. The other kind of igneous 
rock is much harder and more compact, with a total absence of all 
nodules. Mr. Hamilton could not observe any marked line of sepa- 
ration between the two kinds of trappean rock, and therefore does 
net consider it probable that different coulées, some vesicular, others 
without air-, gas- or vapour-cells, flowed over each other. The appear- 
ances described by Mr. Hamilton more resemble, on the great scale, 
_ those igneous products where bands of vesicles occur in a mass poured 
out of some volcanic vent at the same time, portions without vesicles 
alternating with those in which they abound, and which may be seen 
in fragments as small as a hand-specimen. While the rock was in 
a molten state portions became vesicular, and when it was poured 
out, the viscous stream carried the parts in elongated streaks, often 
alternating with each other in minor. portions of the general mass. 
Respecting the agate nodules themselves, they are described as 
varying much in character, colour and substance. The smaller cavi- 
ties are generally quite filled, commonly with a compact chalcedonic 
mass, while those of large size are usually lined with agate layers of 
different colours, and are invariably hollow. The outer layer of the 
large cavities varies in thickness, lined either with interior mammillated 
surfaces or by quartz crystals. 
The mineral contents of vesicles and cavities in igneous and other 
accumulations, these hollows having never had communication with 
cracks or fissures of the rocks in which they occur, furnish us with 
excellent examples of the manner in which silica and other substances 
in solution have permeated through the pores of rocks, even of many 
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