1880 .] 
99 
[Wadsworth. 
the successive layers of minerals. The vapors then, if the source, must 
have continued to rise for some time afterward. But is it possible that 
vapors should rise up through the solid rock ? Such does not happen about 
recent volcanoes; for fissures are first opened and then the vapors escape. 
And could it happen with the water above pressing -down into the rock with 
the force of an ocean even a mile deep ? There may be instances of this mode 
of formation ; but that it should be the usual mode is irreconcilable with 
the many facts stated. * * * * * * * These various facts appear to estab- 
lish infiltration as the principal means by which amygdaloidal minerals 
have been produced.” (Am. Jour. Sci., 1845, (1)xlix. 52-64.) 
In an abstract of the above given paper, in the Proceedings of 
the Sixth Annual Meeting of the Association of American Geol- 
ogists and Naturalists (New Haven, 1845), it is stated, after 
citing facts as above : 
“ These facts find their readiest explanation in the hypothesis of infiltra- 
tion, and many admit of no other explanation.” 
Also concerning the formation of the minerals in question : 
“ Heat may be necessary for the formation of some of them ; yet we can 
not at present fully appreciate the efficiency of chemical agents in a nascent 
state acting slowly without heat during long periods.” (Pages 27, 28.) 
In another paj>er he states concerning amygdules : 
“ I do not attribute these crystallizations in all instances to the same 
period in which the eruption of the containing amygdaloid took place, and 
they may have been formed at a much later period. At some subsequent 
eruption in the vicinity they may have been buried and permeated anew 
with hot siliceous waters, which thus gave rise to the amygdaloidal minerals. 
Some of these minerals are believed to be formed by the percolation of cold 
water through the rock, producing slow decompositions and forming new 
compounds. (Am. Jour Sci. 1843, (1), xlv, 116, 117.) 
Professor Dana, in the three papers just referred to, held that 
the amygdaloidal rocks were erupted at the bottom of the sea, 
and that the alterations were brought about by the waters of the 
ocean heated by the erupted material, and further that these 
alterations might not take jdace then, but through the medium of 
the ocean waters heated at a later eruption, or even by the action 
of cold water. 
