Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/172

162 it is an important observation that there is no correspondence between the irregular form of the bottom and that of the present surface of the country.

Although the number of distinct beds or layers in this basin is very considerable, yet the authors of the memoir have reduced them to eleven principal classes.

Of these the three first above the chalk are of marine origin, and they cover the whole of the bottom of the basin.

The gypsum and accompanying marles they imagine to have been formed chiefly in fresh water, from the fossils contained in them.

The next series of marles and sandstones containing only marine shells, shows the sea to have again covered the last formed strata.

Lastly, the upper freshwater formation demonstrates this place to have been a second time converted into a lake.