652 EEroKT— 1888. 



stratigrapbical, that the Fuller's-earth on the whole is more intimately connected 

 with the Great Oolite than with the Inferior Oolite. For convenience of classifi- 

 cation it should therefore he placed with the Great Oolite series. 



3. Note on the Portland Sands of Sioindon and elsewhere. 

 By Horace B. Woodwaed, F.G.8. 



[Communicated by permission of the Director-General of the Geological Survey.] 



Attention was drawn to some fresh sections at Swindon and these confirmed the 

 sequence made out by Professor J. F. Blake from somewhat scattered data. The 

 sandy beds that yield the Swindon Stone were originally grouped as ' Portland 

 Sands,' but they clearly belong to the Portland Stone division, as pointed out by 

 Mr. Blake. The basement bed here and at Aylesbury consists of a conglomeratic 

 band containing lydites, a few quartz pebbles, and some derived fossils. The true 

 Portland Sands occur below, and are about CU feet thick. The sequence is as 

 follows : — 



feet 

 Portland Stone, with lydite bed at base and in upper part of 

 clay beneath. 



/ 3. Blue and brown clay 19 



2. Sandy calcareous rock. Oyster-bed with small 



Portland J acuminate oyster 8 



iSands. j 1. Greenish and yellowish sauds with huge concre- 

 tionary masses of calcareous sandstone. The 

 \ sands merge downwards into 30 to 40 



Kimmeridge Clay. 



Comparing the sequence with that at Aylesbury, worked out by Mr. Hudleston, 

 we find the Portland Stone with lydite bed at base resting on the Hartwell Clay. 

 This clay, like the Blue and brown clay (No. 3.) at Swindon, was originally taken 

 to be Kimmeridge Clay, but the former has been shown to be on the horizon of the 

 Middle Portlandian of French geologists; and there is no doubt, on stratigrapbical 

 and palseontological grounds, that the clays of Swindon and Hartwell are on the 

 same approximate horizon, and that both belong to the Portland Sands. We have 

 not clear evidence of the sequence beneath the Hartwell Clay at Aylesbury ; but a 

 deep well at Stone, in that neighbourhood, showed the presence beneath the Port- 

 land Stone of Blue clay. Limestone, Dark sand, and then Blue clay again — this last- 

 named bed being, no doubt, the true Kimmeridge Clay, although detailed measure- 

 ments are wanting. 



Doubtless there is some inconvenience in a term like Portland Sands, when it 

 includes prominent beds of clay like those of Swindon and Hartwell, and when the 

 Portland Stone of Swindon is so largely represented by sand. We might employ 

 the terms Upper and Lower Portlandian were it not that on the Continent a three- 

 fold division has been adopted, and the Lower Portlandian embraces beds that in 

 (this country cannot be separated from the Kimmeridge Clay. The Middle Port- 

 landian, as before mentioned, represents our Portland Sands and Hartwell Clay ; 

 and Professor Blake has applied the term Bolonian to these Middle and Lower 

 Portlandian beds. On stratigrapbical grounds it does not appear possible for us to 

 adopt that term, and on the whole the following grouping appears best adapted for 

 the English strata : — 



Upper Portland Beds — Portland, Tisbury and Swindon Stone. 

 Lower Portland Beds — Portland Sands and Hartwell Clay. 



It is true that at Swindon and Hartwell the Lower Portland Beds are more 

 intimately connected, on stratigrapbical grounds, with the Kimmeridge Clay than 

 with the Upper Portland Beds ; but this is not the case on the Dorsetshire coast, 

 where no conglomeratic band has been met with at the base of the Portland Stone. 



