Chap. XVIII.] 
PAL2E0Z0IC EOCKS IN AMEEICA. 
425 
parts of their range, metamorphosed, and in this state extend from Chili on the 
south * through the Eocky Mountains to the north. Even in Texas they have 
been recognized by F. Homer f. Including the quartz-rocks which are asso- 
ciated with them, they constitute the chief matrix of the gold and other metals 
so extensively worked along this great chain (see Chapter XIX.). It has been 
suggested by d'Orbignyt that the huge stratified quartz-bands described by 
Humboldt may be the altered equivalents of the Devonian sandstones, in which 
he detected various characteristic fossil shells; but if doubts be entertained 
whether the quartz-rocks of the Andes may not be of Upper Silurian rather 
than of Devonian age, there can be no hesitation in referring the next deposits 
in ascending order to the Carboniferous or true Upper Palaeozoic group. At 
numberless places, limestones have been observed charged with well-known 
Carboniferous fossils. Several of them, as Productus Cora, Spirifer striatus, 
Athyris Roissyi, &c, are specifically identical with forms that characterize the 
strata of this era in Europe and other parts of the globe. As these rocks are 
associated with, or followed by, accumulations of coal, the general relations of 
this series are clearly Carboniferous. 
We now know, therefore (and the recent explorations in California, Oregon, 
&c, have confirmed the view), that sedimentary deposits of Silurian, Devonian, 
and Carboniferous age constitute some of the loftiest ranges and metalliferous 
plateaux of the American Continent. These were, in ancient times, penetrated 
by granites, porphyries, trachytes, and other eruptive matters; and in the 
modern era they form, in some localities, the seat of active volcanic forces. In 
the sequel it will also appear (see Chapter XIX.) that not merely the Palaeozoic, 
but the Secondary deposits up to the Cretaceous inclusive, sometimes, indeed, 
even to Tertiary formations, have been so strikingly metamorphosed as to re- 
semble much more ancient rocks, and occasionally have been traversed by au- 
riferous veinstones in the coast-ranges of California §. 
To bring, however, the older formations of America into accurate parallel with 
those of Europe, we must quit the chain of the Andes and the high grounds of 
Mexico, and turn to British North America and the vast territories of the United 
States. In large portions of those regions the older strata have been compara- 
tively exempted from igneous disturbances, and geologists have been able to 
demonstrate the order of succession to be the same as that of which numerous 
proofs have been recited in the preceding pages. 
The great fundamental ' Laurentian system ' of Logan, on which all the other 
sedimentary deposits repose, extends westward to the Lakes Winnipeg and 
Superior, and, crossing the St. Lawrence at the Thousand Islands, reappears in the 
Mountains of Adirondack, in the State of New York. Just as the oldest gneiss 
of the north-western coast of Scotland (see diagram, p. 169) is the foundation- 
mass of all the rocks of the British Isles, so on a much grander scale is it the 
oldest rock of the vast western continent. Divided into two masses, the lowest 
and by far the largest of these, in which the Eozoon has been found, has been 
noticed in the First Chapter of' this volume. For the wide spread of the Lower 
Laurentian in British North America, the reader is referred to the admirable and 
clear map published by Sir W. Logan in the ' Eeport of Progress of the Geolo- 
* In the admirable work on South America, h'altnisse, &e.,' 1849. 
by Mr. Charles Darwin (1846), the only Palseo- J See Cordier, ' Eapport a l'Acade'm.ie Eoyale 
zoic fossils alluded to are those of the Falkland des Sciences sur les re'sultats scientifiques du 
Voyage de M. Alcide d'Orbigny dans l'Ame'riqi 
Islands (Upper Silurian? and Devonian), though 
it is probable that some of the clay-slates &c. in 
1.1. . A ni.ii- _ a..j-_ t_ _v.:_v. u_ „j 
du sud, pendant les 8 annees depuis 1826 jusqu'a 
the chain of the Chilian Andes, to which he ad- 1833,' 1842. 
verts, are of older age. § See Whitney's 'Geol. Survey of California.,' 
t Komer, 'Texas, und die physischen Ver- 1866. 
