But this does not
affect the general character of clay; it only forms a special variety in
the subject. A sensible or considerable portion of calcareous earth, in
the composition of clay, constitutes a marl, and a sufficient admixture
of sand, a loam.
An indefinite variety of those compositions of clay form a large portion
of the present strata, all indurated and consolidated in various
degrees; but this great quantity of siliceous, argillaceous, and
other compound substances, in form of earth or impalpable sediment,
corresponds perfectly with that quantity of those same substances which
must have been prepared in the formation of so much gravel and sand, by
the attrition of those bodies in the moving waters.
Therefore, from the consideration of those materials which compose the
present land, we have reason to conclude, that, during the time this
land was forming, by the collection of its materials at the bottom of
the sea, there had been a former land containing materials similar to
those which we find at present in examining the earth. We may also
conclude, that there had been operations similar to those which we
now find natural to the globe, and necessarily exerted in the actual
formation of gravel, sand, and clay.
Pages:
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175