100 Geology of Wiltshire. 
and Nerita costulata, (fig. 9). In many of the lower as well as in 
the upper strata of the series the shells are much broken. The 
middle beds of freestone, or great oolite, are almost wholly a true 
oolite; that is, a rock entirely composed of small rounded grains, 
resembling the roe of fish, which appear to have been formed from 
successive coatings of carbonate of lime upon a nucleus, consisting 
of a minute grain of sand or a fragment of shell. If we imagine 
such small grains to have been kept for some time in gentle 
motion by slight undulatory movements at the bottom of a sea in 
which much carbonate of lime was being slowly deposited, we may 
obtain a notion of the mode in which this oolite rock was formed. 
Near Bradford thick beds of clay occur, interstratified with the 
oolitic limestone beds, and in these are found many Crinoideans or 
stone lilies, with their roots or bases still attached to the rock on 
which they evidently grew undisturbed for years before they were 
enveloped (or, as it were, potted) in the clayey mud, which has 
preserved them for our admiration. The wood-cut below, from Sir 
©. Lyell’s Manual, gives a representation of these remarkable fossils. 
Apiocrinus Parkinsoni, or Pear Encrinite; Miller. Fossil at Bradford, Wilts. 
a. Stem of Apiocrinus, and one of the articulations, natural size. 
b. Section at Bradford of great oolite and overlying clay, containing the fossil encrinites. See text. 
c. Three perfect individuals of Apiocrinus, represented as they grew in the sea on the surface of 
the Great Oolite. 
d. Body of the Ayiocrinus Parkinsoni. 
The slaty or flaggy beds of the Forest marble (much quarried 
for roofing tile) are also often interstratified with clay or sand, 
and their surfaces frequently shew the ripple mark produced 
by the ripple of the waves upon them as they were being deposited 
on what was evidently, at the time, a shallow calcareous and sandy 
