Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/392

382 part is exposed, and corresponds exactly with the smooth cylinders. Having seen this in one complete instance, I was able to trace it in others; and was now convinced that the smooth cylinders were only the internal parts of the same body whose various sections. formed the white circular and elliptical figures.

When these forms are enclosed in a very soft sandstone, although the sections are very evident from their colour, yet they are seldom seen in relief, because the cylinders themselves are soon destroyed by the abrasion of the surface; whereas the hardness of the limestone permits them to remain.

Besides the prodigious quantity of fine specimens of these fossils to be found at the Western lines, Pl. 30, there is another circumstance peculiar to the place, arising from the position of the rocks forming the cliffs. These consist entirely of the green sandstone formation, which has slid down in a mass into the sea at the time when the great failure of the stratum took place which occasioned the under-cliff. The stratification of these rocks dips considerably towards the land, and from the action of the sea on the lower part, large portions have been detached, leaving the upper part overhanging frequently twenty or thirty feet. These masses have separated from the rest of the rock, and exhibit in the divisions between the beds a view of their upper and under surfaces. Attached to these surfaces are vast layers of these fossils heaped upon each other, and lying prostrate in every possible direction, and in fragments of various sizes. Their substance is always sandstone of very soft quality, and having suffered much from the weather, they appear like sculpture almost defaced. It is not difficult however to trace multitudes both of the stems and heads, varying from four inches in diameter to the eighth of an inch. In the joints between the beds where they are still not separated, they may also be