No. 181.] 1^ 
rally abound in them, though their mineral products were in great 
part carried from existing land, made evident not only from the 
circumstance of mud, sand and gravel, being products of agitated 
waters, but from the remains of plants found in the shale and sand- 
stone, and likewise the occasional occurrence of some fresh water 
shells. 
A feature common to all the rocks of the fourth district, is the 
horizontal position to the eye of the strata or layers into which 
they are divided; and being characteristic of the more modern 
class, was the main cause of error in the early classification of the 
rocks of western New-York, as well likewise of the whole range 
west of the Allegany to the Lakes, and from the Hudson to the 
Mississippi. Whereas within these immense limits, with the ex- 
ception of the cretaceous group in the southern part of Tennessee, 
there exist no rock masses in place more modern than the great 
deposition of bituminous coal. Those other mineral products there 
met with belong to the alluvial class. ' These products either line 
the bottoms or sheath the sides of the innumerable valleys which 
intersect the rocks. All the valleys of that extensive region show, 
by the horizontal position and parallelism of the rocks of which 
their sides are composed, that they are valleys of denudation or 
excavation; at the same time they show by their extent, the ex- 
tent of the denudation, and the source of their immense and co-ex- 
tensive deposition of alluvial; and the varied and favorable compo- 
sition of the rocks explains the cause of the far-famed fertility of 
their alluvial soils. 
Besides this cause of error in the classification of these rocks, 
others may be mentioned, more especially appertaining to those of 
this State. These were, a want of knowledge of the fossils they 
contain, and of the importance of this class of characters in the 
determination of rock masses; the presence of coal in many of 
the rocks, though in exceedingly limited quantities; the dark car- 
bonaceous color likewise of many others; the presence of car- 
buretted hydrogen gas — likewise of petroleum, and the occurrence 
of salt water, in that abundance which in Europe is characteristic 
of a more modern class. 
In 1827 and '28, I travelled over a part of western New-York, 
and a considerable portion of the states of Ohio, Kentucky, Ten- 
nessee and Virginia. The extensive collection of fossils, rocks 
and minerals I then made, fully satisfied me as to the greater geo- 
