1880 .] 
101 
[Wadsworth. 
I sustained in an article in Yol. xlix of the first series of this Journal 
(1845), and the various facts I have since observed have tended to confirm 
me in the conclusion. In the paper referred to I attribute the change to 
infiltrating waters. The opinion has many advocates.” (Am. Jour. Sci., 
1873 (3), yi, 107, 108.) 
Again we read : 
“ The cavities in a lava or igneous rock, such as are formed by expanding 
vapors while the rock is liquid, differ from veins in size, but not essentially 
in the method by which they are filled with minerals. In amygdaloids these 
minerals are usually chlorite, quartz, prehnite, datolite, analcite, or some 
of the zeolites, or calcite; and in each cavity they often are in successive 
layers, analogous to the layers of a banded vein. They are introduced by 
infiltrating waters, which derive the ingredients mainly from the inclosing 
rock, through the decomposition of some of its minerals. ****** 
Most of the species in amygdaloidal cavities are hydrous, — showing that 
they were formed at a much lower temperature than the materials of a 
granytic vein; and some of them may perhaps be formed even at the 
ordinary temperature.” (Manual of Geology, edition of 1874, page 734 ; 
see also edition of 1862, pages 715, 716.) 
Again : 
“ It seems to be quite certain that the chlorite in the above mentioned 
porphyry, and in igneous rock generally, was not only derived from ingre- 
dients in the rock, but was made through the agency of water that gained 
admission from some subterranean source when the melted rock was ascend- 
ing to the surface ; that the same is true fcr ether hydrous minerals dissem- 
inated through the mass of any igneous rock, for example, the zeolitic, in 
phonolytes. The same kind of evidence sustains, * * * * * the conclu- 
sion that all amygdaloidal rocks owe the cavities which they contain (the 
cavities occupied by the amygdules), and a large part of the zeolitic and 
other minerals in the cavities, mainly to the action of the same waters on 
the rock — first while melted and then while cooling from a state of fusion. 
Further, such waters may have carried into the cavities not only hydrous 
minerals, but also anhydrous. ******** If cavities exist they are 
sure to become filled, because all solutions would pass into them and keep 
depositing until they were full ; and the rock, if the cavities were numerous, 
might thus be drained of a large part of the minerals formed, the chlorite 
excepted. These cavities have no doubt sometimes received mineral 
material from infiltrations of later date, but not so the body of the rock.” 
(Am. Jour. Sci., 1775 (3) ix, 59.) 
