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

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Mr. Webster on the Strata lying over the Chalk.

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.

  1. Chalk.
  2. Plastic clay.
  3. Coarse limestone and sandstone.
  4. Silicious limestone.
  5. Gypsum and marl, containing bones of animals, forming the lower freshwater formation.
  6. Marles of marine origin.
  7. Sand and sandstone without shells.
  8. The superior marine sandstone.
  9. Buhr or millstone formation without shells, and argillaceous sand.
  10. The upper freshwater formation, comprehending marles and buhrs with freshwater shells.
  11. Alluvium or earth of transportation, both ancient and modern, analogous to our gravel, &c. comprehending rounded pebbles, pudding stones, argillaceous marles and peat moss.

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.