H. B. Woodward—Notes on Jurassic Rocks. 469 
IV.—Nore on tHE PortLanp Sanps oF Swinpon AND ELSEWHERE. 
By Horace B. Woopwanrp, F.G.S., of the Geological Survey of 
England and Wales. 
[Communicated by permission of the Director-General of the Geological Survey. ] 
TTENTION was drawn to some fresh sections at Swindon, and 
A these confirmed the sequence made out by Prof. 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 60 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 acuminate oyster... 8 
Sands. | 1. Greenish and yellowish sands with huge concre- 
tionary masses of calcareous sandstone. The 
sands merge downwards into ... ... ... ... 30 to 40 
Kimeridge 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. 8) at Swindon, was originally taken to be Kimeridge 
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 
stratigraphical and paleontological 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 
Portland Stone of Blue clay, Limestone, Dark sand, and then Blue 
clay again—this last-named bed being, no doubt, the true Kimeridge 
Clay, although detailed measurements 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 threefold division 
has been adopted, and the Lower Portlandian embraces beds that in 
this country cannot be separated from the Kimeridge Clay. The 
Middle Portlandian, 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 strati- 
graphical grounds it does not appear possible for us to adopt this 
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. 
