No. 275.] 
269 
In the examination of nearly every quarry in the three counties, these 
were the facts observed. The lower range of '^plaster beds" are en- 
closed in a dark coloured, and to appearance, a somewhat altered mass, 
in which I was informed that Dr. Beck had found 20 per cent of mag- 
nesia in an analysis made from that of the Nine Mile creek. Resting 
upon this mass is the series which contain the hopper cavities, noticed 
by Mr. Conrad, and Dr. Beck particularly. Also the porous or " ver- 
micular rock," and the organic remains. These latter I could only find 
in one position and in two localities. The porous rock seems to be 
disposed in two different ways. In one forming a bed, holding a posi- 
tion more or less fixed, and apparently extending over a large portion 
of the gypseous region. In the other, the masses are limited in extent, 
without fixed positions, appearing to have been deposited at irregular 
intervals. 
The cavities of these porous rocks have no analogy whatever with 
those derived from organic remains, nor are they referrable to any po- 
rous rocks other than those of volcanic origin, and I should suppose that, 
were they not composed of carbonate of lime chiefly, but of the usual 
siliceous and argillaceous materials, the igneous origin would have been 
given to them by their first describer. 
The common opinion that the plaster is still growing, is set at naught 
by the fact, that it is as fully formed where alluvial soil covers its 
masses, as it is where layer on layer of its own deposit is heaped upon 
it. No difference can be perceived in either. No increase, I should 
suppose, could have taken place since that period when it rose from the 
deep, to which it had been depressed by the masses which originally 
were deposited upon it, and which subsequently have been swept away. 
The arching over the gypsum is readily explained from the facts 
which experience with "water limes" have given to us; and a fact 
noticed in a quarry of water lime, south of Chittenango, verifies that 
experience. That certain materials or mixtures will harden or sett, 
when others will be soft and yielding, may be considered fully esta- 
blished by the many experiments made with good and bad water limes, 
and by subalances taken for such, and likewise that there is a difference 
in the time of setting of the different kinds. This is admirably shown 
in a layer of water lime back of Chittenango. The layer was about eight 
inches in thickness. The note I made was this: " Some parts of a 
course of water lime show a local disturbance, by which it is evident 
that a derangement can go on which extends but to a little distance 
from the action, and show that the parts disturbed were the first to ag- 
