Crosby.] 482 [April 7, 
rocks on the continent — folds, faults, and igneous extrusions on a large 
scale having conspired to complicate their structure and alter their 
lithological aspect. And what is the result? Nowhere in the Bos- 
ton basin do we find a vestige of indisputable evidence pointing to 
the conclusion that there are crystalline rocks of Paleozoic age in this 
part of New England. Every crystalline rock in this region is repre- 
sented in the pebbles of the conglomerate, and this rock certainly un- 
derlies the slate. Only in a few limited localities, where the slate 
and conglomerate have been altered by contact with intrusives — 
as at Nantasket, Weymouth, Brighton, and Nahant,—is it possible 
to trace any lithological resemblance between these and any crystal- 
line rocks; and in all such instances the cause and local nature of 
the alteration are clear beyond dispute; and, furthermore, the altered 
rocks bear no likeness to any crystallines in this region, save where 
arenaceous layers in the conglomerate have the hardness of quartz- 
ite (and induration is the simplest species of alteration), or slate and 
sandstone have the texture of amygdaloid. In this last case, how- 
ever, there is really no resemblance; for the very large amygdules 
developed locally in the slate at Mill Cove, in Weymouth, and East 
Point, Nahant, are entirely unlike anything observed in the true 
amygdaloid of the Boston basin. In short, crystalline characters 
are, practically, entirely wanting in the Primordial beds of eastern 
Massachusetts, notwithstanding these have at many points suffered 
an extreme degree of disturbance. 
Probably the best test of the naturalness of the Eozoic divisions 
is that afforded by their greater or less universality. If the litholog- 
ical groups or facies corresponding to the names Laurentian, Huro- 
nian, etc., are found to be persistent over an entire continent or 
hemisphere, and to preserve everywhere the same stratigraphical 
relations, giving an invariable sequence, then these important geolog- 
ical inductions must be considered as resting on a broad and firm 
basis of facts. 
Comparisons of the stratified crystallines of North America and 
Europe have been instituted at various times, chiefly by Dr. Hunt; 
and in not a few instances important correlations have been reached, 
In fact, the equivalence, in a general way, of a large proportion of 
the Eozoic récks of the two continents may be considered as pretty 
definitely settled. Nearly, if not quite, all the North American 
divisions are recognized in Scandinavia; and there can be little 
doubt of the existence in central and southern Europe of more or 
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