256 Mr. Lonsdale on the Oolitic District of Bath. 



1 . The top bed of clay is of a pale grey colour, rather smooth to the touchy, 

 and effervesces with acids. The lamina of grit contain a considerable propor- 

 tion of calcareous matter. At Norton St. Philip it incloses near its upper 

 part a stratum of rubbly, indurated marl, abounding with fragments of a small 

 Ostrea and Terebratulae. 



2. The sand and sandstone appear to be the representative of the Stones- 

 field slate of Oxfordshire. The sand which sometimes forms the greater part 

 of the bed, but which sometimes is almost wanting, is of a very fine grain, 

 and varies in colour from reddish brown to almost white. It is occasionally 

 mixed with a small cjuantity of clay or lime, and then becomes a friable sand- 

 stone, alternating in thin beds with a calcareous grit. Layers and irregular 

 beds of clay likewise often occur associated with the sand. The sandstone or 

 grit forms, either large spheroidal masses aggregated together and contained 

 in the sand, or tabular strata. The true pot-lid shape is of rare occurrence, 

 and appears to be confined to Ridge near Beckington. The stone possesses 

 a tendency to split into thick flags parallel to its position in the bed, but never 

 into thin tiles. The cross fracture is splintery, and in general exhibits small^ 

 shining, parallel facets. The grain of the grit is for the greater part exceed- 

 ingly fine, though it not unfrequently acc[uires an oolitic character; and in 

 the same specimen one portion will be a sandy oolite, and the rest a calca- 

 reous sandstone. Patches, or small almond-shaped nodules of soft clay are often 

 imbedded in, the stone; and on being removed, by exposure to the weather, 

 the emptied cells give it a vesicular appearance. Organic remains are not 

 universally disseminated through the grit, but in some localities they are suf- 

 ficiently numerous to compose the principal part of the block or stratum, and 

 convert it into an impure, shelly limestone. All the varieties of the grit 

 effervesce very strongly. The prevailing colour is pale brown, but some of 

 the beds are of a deep blue. 



3. The clay is of a pale brown colour, is slightly calcareous, and contains 

 patches of a hard, closely grained, shelly limestone sHghtly oolitic, and laminae 

 of calcareous sandstone or grit. It is occasionally wanting. 



4. The shelly limestone or coarse oolite is the bed to which the term forest 

 marble is peculiarly applied. The prevailing fossil, a small species of Ostrea, 

 is occasionally so abundant as to constitute the greater part of the stone ; but 

 it is oftener more sparingly diffused through it. The basis by which the 

 organic bodies are united is frequently composed of crystallized carbonate of 

 lime, though sometimes of a yellowish or bluish marl, and sometimes of a pale, 

 earthy limestone. Oolitic particles are more or less numerous in each variety. 

 Some of the beds are of a close texture, tough and heavy ; others are porous. 



