§ 3. Lower Freshwater Formation.
This formation is to be seen most distinctly in the section of the hill called Headen, which forms the northern boundary of Alum bay, in the Isle of Wight. It appears there in a series of beds of sandy calcareous and argillaceous marls; sometimes with more or less of a brownish coaly matter. Some of them appear to consist almost wholly of the fragments of freshwater shells, many of which are however sufficiently entire to ascertain their species. These are the lymneus, planorbis and cyclostoma, and perhaps the helix; with a bivalve resembling the freshwater mytilus.
These beds lie immediately upon the black clay that covers the white sand, described in the account of Alum bay. They are extremely irregular, and are not to be traced distinctly from each other for more than about a few hundred yards, the remaining part being so hid by the mouldering slope, that the formation can only be observed in mass. It may be seen however extending round the north side of Headen into Totland bay, where it forms the upper part of the cliff: and at the point called Warden-ledge, it is found in a more uniform and indurated state. Here, when the clay upon which it rests gives way from the rain and frost, large masses of it fall down, which are employed for the purposes of building, though the stone is not of a good quality. Pursuing it farther into Colwell bay, it dips to the north, and is soon lost; nor is it to be seen any more on that side of Yarmouth. At the bottom of these beds, and between them and the black clay, there is frequently a layer of two inches or more in thickness of a dark brown coaly matter, much like what is usually found at the bottom of peat bogs, and it appears to be a similar substance that tinges many of the beds.