basalt is covered in places with a baked basaltic tufa or conglom- 
erate, in some parts red and jaspery, and containing ragged masses 
of basalt, just as they were torn from the melted rock by the agi- 
tated waters. ‘3 ar 
The material of the metamorphic porphyries in the Andes was 
never clay like common clay deposits: it is merely fragmented 
or pulverized porphyry or basalt, either thrown out as a sand 
eruption, which is barely possible ; or secondly, shivered from the 
rock while in fusion by contact with water ; or thirdly, produced 
by subsequent abrasion. ‘They underwent little if any decom- 
position before they were rehardened into rock, for as remarked, 
such decompositions go on but slowly if at all in cold water. 
Let ts now turn to the granitic series of rocks, and follow 
where analogy leads. Granite like porphyry is an igneous rock. 
In its era, granite sands were formed like porphyry sands, and 
restored by heat to metamorphic granite like metamorphic por- 
phyry. Such are our conclusions. I use the word granite here, 
as a general term for this and the associated rocks, gneiss and 
mica slate, syenite and hornblende slate, &c. which I have 
shown may also be of igneous origin. These granite sands, like 
porphyry sands, were formed about the region of eruption in one — 
of the modes pointed ‘out, arid in all probability were never clays, 
like the alluvial deposits of the present day. It has been too 
much the effort to make these schists out of common clays, and 
Boase, in his valuable work on Primary Geology, derives an ar- 
gument against the metamorphic origin of the schists, from the 
fact that common argillaceous shales contain no soda or potash. 
But this argument will not. hold if the view proposed be correct. 
But let us trace out some of the changes which we may show 
to have thus taken place in the rocks now crystalline. 
‘The change of deposited limestones to granular limestones has 
occurred in all ages of the globe, and is attributable, as in other 
metamorphic changes to heated waters, except in some instances 
where the alteration is confined to within a few feet of an igne- 
ous rock.- With regard to primary limestones, a general survey 
of the facts, seems to evince that some of these were of igneous 
origin, like granite. If this were the case there must have been 
others of a sedimentary character formed at the same time with 
the deposits of granitic sand, and through the action of the same 
causes. ‘These were recrystallized by the next discharge of heat- 
ed waters. 
] fodern Igneous Rocks and the Primary Formations. 119 | 
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