Mr. Lonsdale on the Oolitic District of Bath. 267 



green-sand. They occur between Great Clieverell and Worton, and near 

 Cuckold's Green. The sand is ahnost universally friable. 



a. The calcareous grit appears at Heddington Wick, and near the top of 

 the formation. It is composed of thin lamina of a reddish white colour; it 

 is tolerably soft^ and is imbedded in sandy clay. 



b. The sandstone is displayed only at Crockwood Mill near Urchfont, where 

 it forms two strata immediately under the g-alt. It consists of rather coarse 

 grains of quartz cemented by carbonate of lime, and contains many, very small, 

 polished particles of brown iron ore. Fragments of a large Pecten, with 

 nearly equal ears, are common in both strata. The natural divisions between 

 the blocks of stone are generally coated with crusts of argillaceous carbonate 

 of iron. 



c. The conglomerate is composed of pebbles of quartz cemented by a 

 highly ferruginous sand. The pebbles are generally small, seldom attaining 

 an inch in diameter, and are very unequally dispersed through the basis : 

 sometimes they form the greater part of the mass, but at others are almost 

 wanting. The oxide of iron, forming the cement, is frequently so abun- 

 dant as to constitute a rich ore, which was formerly smelted to a considerable 

 extent. The conglomerate seldom possesses any great degree of hardness, 

 but yields with facility to the hammer, and appears occasionally as a loose 

 rubble, locally called gravel. The colour of the basis is a deep brown, and 

 that of the pebbles white. The blocks of which the conglomerate consists 

 are imbedded in an irregular manner in the sand. 



d. The spheroids are formed of concentric crusts of iron-stone, either in 

 contact, or separated by zones of sand, and have a nucleus of loose sand or 

 sandstone. They occur chiefly at Seend and Griffin Lane, and are either 

 placed in juxtaposition, when they interfere with each other's form, or are 

 parted by layers of sand. 



e. Chert is comparatively rare in the lower green-sand ; but a stratum con- 

 taining the casts of an Astarte, aTrigonia, and a Natica, is occasionally worked 

 near Greenland's Farm ; and close to Crockwood Mill is a cherty sandstone 

 with green particles. 



Organic remains have hitherto been observed by me at only two localities; 

 the one just mentioned, and Lockswell Heath, where casts of a beautifully 

 imbricated Patella, and three or four species of bivalves, are to be found in a 

 bed of the quartzose conglomerate. 



The extent of the lower green-sand in Wiltshire is limited ; and between 

 Calne and Great Cheverell, the southern boundary of its range, it has been 

 removed in many places by denudation. In the neighbourhood of Calne it 



2m2 



