BniTISII ASSOCIATION MIOIOTING. 
803 
tlio opinions of Fitlon, Conybcaro, and more recently of Professor PliiUipri, 
who on a previous oceasiou had stated reasons strongly in favour of tue 
Wealden age of these beds, the course adopted by the geological surveyors 
could only be considered provisional. 
ON THE BLENHEIM IRON-ORE AND THE THICKNESS OF THE 
FORMATIONS BELOW THE GREAT OOLITE AT STONESFIELD, 
OXFORDSHIRE. 
By Edwahd Hull, B.A., F.G.S. 
TIic economic importance of the Liassic and Oolitic iron-ores is yearly on 
the increase, owing to three causes — the expansion of the British iron-trade ; 
the local curtailment in the supply of the clay ironstone of the coal-measures ; and 
the extension of the railway system, which has rendered available iron-ores far 
removed from the boundaries of the coal-fields, and which were almost unknown 
till witiiin the last fev/ years. From the "Mineral Statistics of Great Britain," 
collected by Mr. Hunt, it appears that in 1S57 the quantity of ore raised from 
the Cleveland, Whitby, and Northamptonshire districts reached the amount of 
Bcavly one and a-half million of tons, or nearly one-tenth of the total quantity 
raised in Great Britain. It may safely be predicted that ere long Oxfordshire 
will also rank as an iron producing county. 
Blenheim Iron-Ore. — The existence of highly ferruginous beds in the 
direction of Banbury and Deddington has been known for some years back, 
and tliey have to a small extent been quarried for smelting. There are two 
varieties, a siliceous ore, occurring at the top of the sands, which form the lower 
zone of the Great Oolite, and a calcareous ore, forming tlie upper rock-bed of 
the marlstone, or Middle Lias. Dm-ing tlie progress of the Geological Survey 
in the neighbourhood of Woodstock, the existence of this latter ore was ascer-- 
tained in several places, but in particular along tlie valley of tlie Cherwell, 
west of Charlbury.* 
Geological position. — The Blenheuu ore is identical in geological position and 
almost m its nature with the Cleveland ore of Yorksliire. It forms the rock- 
bed at the top of the Marlstone, which in Gloucestershire and elsewhere pro- 
duces the tabulated promontories which jut out from the flank of the oolitic 
escarpment. At Fawler it rests upon soft sands, comprising the lower division 
of the Marlstone, and is sunuounted by the clay of the Upper Lias. It varies 
in thickness from ten to fifteen feet, and is of nearly uniform composition through- 
out, except where there occur bands of fossils, with an excess of carbonate of lime. 
The shells are Marlstone species, as Rhi/tichoiiella tetrahedra, Terebraiiila punc- 
tata, &c. 
Mineral character. — At the outcrop the rock presents a rich ferruginous 
aspect, but when reached at positions where it has been protected from 
atmospheric influences, its colour is deep olive green ; and the gradual change 
may be observed in blocks newly split. In its latter state it appears to be 
oolitic under the lens. 
The cliaracter of the ore, before oxydization is probably that of carbonate 
and silicate of iron, the latter imparting the green tinge : when exposed, it 
passes into a iiycbated peroxide of iron. The quantity of silica is about 12 per 
cent., and of lime 10 per cent. Phosphoric acid is only present in minute 
* As this ore extenda rnidor the property of the Dnke of Marlhorough, I have called it 
" Blenheim ore ;" and for further details refer to the " Geology of the countiy roimd Wood- 
stock." Mem. Geol. Survey : 1857. 
