208 G. H. Cooke on the probable Age of the White Limestone 
lakes and other large bodies of water breaks up in the spring. 
The presumption is that all ice forming on water is produced in 
the same m But at a very low temperature, the crystalli- 
zing centres are so many and the freezing of the plates and 
intervening spaces so rapid, that the process could not be dis- 
tinguished. Yet all field ice from this latitude to the arctic 
regions breaks up in the same manner, by first becoming porous 
or “rotten.” 
Cooks, Prof, of Chemistry, &., New Brunswick, N. J. 
Dear Sirs,—At our late visit to Franklin Furnace, Sussex Co., 
N. J., I had the pleasure of pointing out to you, the faithfulness 
of Vanuxem and Keating’s original description of the geological 
oceurrence of the rocks of that locality; and the correctness of 
their conclusion, that the white and blue limestones found there, 
are of different ages. Since their description was written it has 
been asserted that the white limestone is of the same age as the 
~ limestone, though changed in appearance by metamorphic 
action. 
Being confident that the facts cited prove the correctness of the 
former conclusion and the consequent incorrectness of the latter, 
I quote portions of the paper which bear upon the above points. 
e original article is published in the Journal of the Academ 
of Natural Sciences, Philadelphia, vol. ii, p. 277, and is entitl 
“On the Geology and Mineralogy of Franklin, in Sussex C0. 
N. J., by L. Vanuxem and Wm. H. Keating.” They say, ‘The 
whole country to a great distance is composed of what ma bp 
considered as sienite. . . . The sienite of Franklin is found 12 
beds or layers of variable thickness, running in a direction The 
allel to that of the ridge from the N.E. to the S.W. -- - 43% 
