24 
must at that time have existed. The whole flora was so 
similar to that of the United States to-day, that it is hardly 
necessary, or possible, to draw a sharp line of distinction 
between the two. The approach of the glacial period drove 
all this vegetation gradually southward, upon both conti- 
nents; but the great geographical differences of Europe and 
America are strikingly shown in the subsequent results. 
In this country, the Miocene plants, which had retreated 
before the ice to lower latitudes, and had there lived during 
the cold period, returned again at its close, and gradually 
overspread, once more, much of their old home. But abroad, 
the retreating flora was driven up against the impassable 
barriers formed by the great East and West mountain ranges 
of Southern Europe and the Mediterranean: thus it died 
out; and, the old land connection with America having never 
been restored, the Miocene flora is scarcely represented in 
Europe now, its place being taken by a different vegetation, 
which came in from Western Asia, after the glacial era had 
passed. 
Pror. D. S. Martin exhibited a series of specimens from 
northern New York, consisting of crystallized quartz and 
apatite, with the edges and angles rounded, associated in some 
cases with calcite, and in others with loxoclase feldspar, 
having the angles sharply defined. Remarking upon the 
idea that has been current, that this rounding of angles is an 
evidence of the action of heat, he pointed out that the loxo- 
clase specimen alone would show the error of this view, as 
in it the feldspar crystals are unaffected, while the far more 
infusible quartz is so rounded as to resemble rock-salt that 
has been wet. 
In all these cases, the evidence is clearly, as Prof. Hunt 
has pointed out, in his paper on the Laurentian limestones, 
that chemical agents, and not heat, have been concerned in 
producing these effects; that solution, and not fusion, is the 
cause. Dr. Hunt has shown that certain alkaline solutions, 
which haye no action on feldspar or pyroxene, attack both 
quartz and phosphate of lime, and that this is the only ex- 
