270 T. 8. Hunt—RHistory of Pre-Cambrian Rocks 
and plutonist schools, neither of which, it is maintained, ex- 
presses correctly the present state of our knowledge. In oppo- 
sition to both of these are the views taught for the last twenty 
years by the writer, and now accepted by many geologists, 
which may be thus defined :— 
1st. All gneisses, petrosilexes, hornblendic and micaceous 
schists, olivines, serpentines, and in short, all silicated crystal- 
line stratified rocks, are of neptunean origin, and are not prima- 
rily due to metamorphosis or to metasomatosis either of ordi- 
nary aqueous sediments or of volcanic materials. 
9d. The chemical and mechanical conditions under which 
these rocks were deposited and crystallized, whether in shallow 
waters, or in abyssal depths (where pressure greatly influences 
chemical affinities) have not been reproduced to any great ex- 
tent since the beginning of paleozoic time. - 
. The eruptive rocks, or at least a large part of them, are 
softened and displaced portions of these ancient neptunean 
rocks, of which they retain many of the mineralogical and lith- 
ological characters. 
IL. Tae History or Pre-Camprian Rocks 1x AMERICA. 
Coming now to the history of our knowledge of American 
erystalline rocks, we find that the lithological characters of the 
Primary gneissic formation of northern New York were known 
to Maclure in 1817, and were clearly defined in 1832, by Eaton, 
who, under the name of the Macomb Mountains, described 
what have since been called the Adirondacks, and moreover 
distinguished them from the Primary rocks of New England 
mmons, in 1842, added much to our lithological knowledge 
of the crystalline rocks of northern New York, but regarded 
the gneisses, with their associated limestones, serpentines and 
iron-ores, as all of plutonic origin. Nuttall, who had previously 
studied the similar rocks in the Highlands of southern New 
York and New Jersey, had, however, maintained, as early a8 
1822, that these had resulted from an alteration of the adjacent 
and ended by doubting whether a great part of what be haa 
escribed as Primary was not to be included in his Metamor- 
phic class. The subsequent labors of Kitchell and of Cooke 
