PORTLAND BOCKS OF ENGLAND. 211 



sooner from the ocean, and, moreover, more rapidly ; hence the 

 regular deposits reached only to the " basal sands." Then incursions 

 from the land produced the strange melee of the beds a to d, as sug- 

 gested by Mr. Godwin- Austen ; and finally the newly risen Portland 

 was carved out by the river whose course is still marked in the 

 quarry. The more gradual elevation of the south left time for 

 the deposition of the AVhitbed and the E,oach; and when the sea was 

 finally expelled its place was taken by a large shallow lake, ofttimes 

 dried up, and during portions of the minor oscillations supporting 

 forests of cycads and conifers, whose growth on the spot, well known 

 there, is sought for in vain at Swindon. We are led, therefore, 

 to this apparently strange conclusion, that the freshwater strata of 

 Swindon, though unconformahle to those beloiv, and representing the 

 FurbecJc in the order of events, are prolahly in jpoint of actual time 

 as old as some parts of the Portland. This conclusion will be found 

 confirmed by a study of the districts further north. 



iS'o. 4. Below the limestones at Swindon, and for some way round, 

 is a very stiff clay, which rapidly breaks down on exposure to the 

 weather. It is very retentive of water, and makes a base for the 

 wells of the town and for the reservoir to the south. I have seen it 

 in several places ; but in only one, a newly-made well in the town, 

 were any fossils obtainable. These were Trigonia incurva or Pellati, 

 Perna Bouchardi, Mytilus autissiodorensis, Corhula dammariensis, 

 Area Beaugrandi, and Cyprina elongata — a fauna which decides 

 their correlation with the Portland Sand. I have not seen the 

 true thickness ; but it was reported to me as 20 feet, which must 

 be a maximum. It will be remembered that just such a clay 

 precedes the shelly limestones in the Isle of Portland. This clay, at 

 Swindon, has unfortunately been mistaken for the Kimmeridge Clay, 

 which has had the effect, first, of inducing the reference of the rocks 

 above to the Portland Sands, and, secondly, of causing a neglect of 

 the underlying beds. It was to the latter that Dr. Pitton alluded 

 when he wrote of the Portland Sands, though they appear to have 

 been not well exposed in his time. 



IN'o. 5. This bed is so well exposed in road-sections to the north and 

 west of the Swindon hiU, and contains so interesting a fauna, that 

 it is extraordinary that it should have attracted so little attention. 

 As seen in the great road-cutting on the north slope of the toTVTi, its 

 upper part is a sandy glauconitic clay, fuU of fossils, and the lower 

 part is a regular lumachelle of Exogyra hruntrutana. The total 

 thickness is not here seen, but it must be more than 6 feet. On the 

 western slope of the hill there is another road-exposure of these and 

 the beds below. Here the present portion is a sharp ferruginous 

 sandstone of brown colour, very irregular in its manner of lying, as 

 though near its termination. It occupies, however, the same 

 position, and must be a modification of the other form ; Dr. Fitton 

 alludes to a third form of it. The fossils also are somewhat different, 

 and the oysters scarcely make a lumachelle. These beds have not 

 been half searched ; they would yield a very largo fauna. A few 

 hours on different occasions have produced the following : — 



