266 Mr. Lonsdale on the Oolitic District of Bath. 



Between Pinhill's Farm and Locksvvell Heath the Kimmeridge clay has been 

 removed^ but at the latter locality it appears as a thin bed underlying the 

 lower green-sand, and may be traced along both the eastern and western 

 sides of the heath, and from Bowden Hill, by Spy Park, to Westbrook, and 

 Nonsuch. At Bromham the formation is wanting, the lower green-sand being 

 in contact with the calcareous grit. Near Rovvde Hill it reappears as a very 

 thin bed ; and at Rowde Wick Farm it begins to assume an important feature 

 in the geological structure of the country. From that point the western boun- 

 dary follows the brook to the Kennet and Avon Canal, then passes around 

 the western side of Seend Hill, and afterwards by the east of Hender's Copse 

 to Keevil, Rey Down, Dunge, Heywood House, Westbury Field, Penleigh, 

 and Dilton : the eastern boundary ranges from Rowde Hill by Smy thick's 

 Farm, the western brow of Polshot Green, Polshot, and Five Lanes, to 

 Cuckold's Green. At this point its continuity is interrupted by several over- 

 lying- strips of the lower green-sand; but from Earl Stoke it describes a 

 line by Coulston, Hud Mill, Westbury Mill, and Penleigh Mill to Dilton. 

 Beyond this villag-e the formation cannot be distinctly separated from the 

 Oxford clay, on which it immediately reposes. In the lane leading- from 

 Dilton towards the Marsh, I found fragments of Oslrea dcltoidea. 



The greatest breadth of the Kimmeridge clay is from the neighbourhood 

 of Baldham Mill to Coulston, a distance of rather more than three miles. 



The thickness of the formation has never been ascertained in that part of 

 the district where its superficial extent is most considerable. 



Lower Green Sand. 



The formation which is now to be described was considered, until the late 

 investigations in the south-west of England, as a portion of those arenaceous 

 beds to which the general term " iron-sand" was applied. The accompanying- 

 table exhibits the leading characters of the lower green-sand of Wiltshire. 



Sand contain. . u 

 ing beds of ) (/ 



_e 



Calcareous grit with sandy clay. . • • ") 



Sandstone j 



Quartzose conglomerate 



Spheroids ofconcentric crusts of iron 



stone 



Chert 



"Ileddington Wick. 

 Crockwood Mill near Urchfont. 

 i „„ , J Lockswell Heath. 



I Seend. Griffin Lane, summit of 



j Bowden Hill. 



LNear Greenland's Farm. 



The sand, of which the formation is principally composed, consists of sili- 

 ceous particles, which vary considerably in their size ; and it often incloses 

 quartzose pebbles. The colour is generally yellow, but is occasionally pale 

 brown, and sometimes light greenish grey, or dingy yellowish green. The 

 two latter varieties bear considerable resemblance to some portions of the upper 



