Dr. FiTTON on the Strata below the Chalk, 267 



Ft. In. 



5. Alternate ranges of sand and stone. 



a. Sand, in many places cream-coloured, abounding in fragments of shells, which ■ 



decompose into a white powder. This includes h 



h. Stone, resembling that of the Portland formation in the Isle of Purbeck, evidently 

 nothing more than sand consolidated by calcareous matter. The masses, when 

 discrete, are of very irregular figure. The stone becomes more abundant in 

 descending ; and near the bottom contains very large Ammonites, A. hiplex, 



A. siganteus 



■20 



Total about 30 



A depth of about six feet below the bottom of this quarry is said to consist of similar sand and 

 stone. 



Portland Sand. — The lower part of this formation is well displayed in an old quarry on the 

 northern brow of Swindon Hill, near the letter B of the word Bowling-green in the Ordnance 

 Map. The rock consists of rough sandy stone, of a dull bluish grey colour, like that of the 

 upper part of this formation in the Isle of Purbeck, in which are included traces of several fossils 

 converted into carbonate of lime ; — Ammonites hiplex, Perna quadrata, Trigonia gibbosa, Trigonia 

 claveltata; with numerous dark particles of silicate of iron, and worn fragments of black chert or 

 flint, many of them evidently the remains of casts of bivalves (some having the outline of a 

 Venus or Lucina ?), and of Ammonites. 



Another form which the Portland-sand assumes here, is that of great nodules of hard greenish 

 and grey calciferous grit, precisely resembling those of Shotover Hill, and of the French coast, 

 especially near Cape Grisnez, — and, as at those places, imbedded in grey sand : above which, 

 is another bed of sand without nodules, containing green particles and numerous fragments of 

 black chert. Mr. Lonsdale had long since mentioned to me these great masses, several of 

 which were then visible on the east of the road from Oxford, close to the town ; but when I 

 visited the place, the greater part of them had been broken up and removed. Immediately 

 below the nodules were about four feet of grey sand. 



The Portland-sand extends westward from the town of Swindon, and occupies a part of the 

 descent of the hill at Okus and Westleaze, where the high ground overlooks the canal. In the 

 farm-yard at Okus were several large nodules, like those above mentioned*. 



Kimmeridge clay. — At the Bowling-green the sand with concretions appears on the surface 

 as the hill descends, and is succeeded abruptly by dark clay, in which I found fragments of 

 oyster-shells ; and this is the case also beneath the great nodules near the road from Swindon 

 to Oxford. I have no evidence of the identity of this clay with that of Kimmeridge, but the 

 facts here stated. 



(142.) List of Fossils from the Strata below the Chalk, in part of North 



Wiltshire. 



\_Upper Green-sand.'] 

 Ammonites dentatus. Rowde Hill, near Devizes. 



A varians. Near Swindon; (in the Chalk marl). 



Mi/a mandibula. Devizes Canal. 

 Panopceaplicata} Rowde Hill. 



* Toothill, a small eminence, which is conspicuous from this place, consists of clay, as also the hill 

 at Elcomb-house. That of Chaddington, still further west, is said to be capped with sand. 



