12 
THE GEOLOGY OP AUCKLAND. 
certain platonic rocks of eruptive character. But I am now 
stating only general principles, and therefore avoid all questions 
leading to scientific discussions. 
The next in order are the Aqueous rocks—the production of 
watery action. They are also called sedimentary rocks, from the 
fact that they are the hardened sediments accumulated at tne 
bottom of the sea or of fresh-water lakes. They are stratified, 
or divided into distinct layers of strata : as, for example, clay- 
slate, marl, sandstone, limestone, and are divided into three 
kinds, called arenaceous or siliceous , argillaceous or clayey, and 
calcareous or chalky— according to the respective predominance 
of silica, alumina, or lime. Bocks of this class cover a laigei 
part of the earth’s surface than any others, and are of the greatest 
interest on account of the organic remains which are found 
imbedded in the different strata. 
There are two principal means of ascertaining the relative age 
of aqueous rocks—derived, the one from their position, the other 
from the fossil remains they contain. 
With reference to position —the bed which lies uppermost is 
of course the newest of all, and that which lies at the bottom, 
the most ancient. 
With reference to the fossils, it is not so easy to give an 
explanation in few words; but some idea may be formed from the 
well-ascertained fact, that certain animals have existed for a 
certain period, and then wholly disappeared and been succeeded 
by other animals ot a different species, which, in turn, have again 
given place to others. 
So, as Sir Charles Lyell truly says, “ a series of sedimentary 
formations is like volumes of history, in which each writer lias 
recorded the annals of his own times, and then laid down the 
book with the last written page uppermost.” -And the organic 
remains are, as Dr. Mantell beautifully expresses it, the “ coins 
of Creation,” which give us the means of tracing the history of 
the development of the organic kingdoms. 
Thus, by superposition and by their organic remains, the 
aqueous rocks are divided into groups forming, in reference to 
their age, what is termed an “ ascending series,” or beginning 
with the oldest, in the following manner 
