82 REPORT— 1860. 



outcrop being traceable for some distance along both banks of the river. It is 

 identical in geological position with the Cleveland ore of Yorkshire, and similar in 

 its mineral character. The bed varies in thickness from 10 to 15 feet, and the ore is 

 capable of being worked to an unlimited extent by tunneling into the hilly side from 

 the outcrop. The fossils, which are local, consist of the usual Marlstone species, as 

 Rhynchonella tetrahedra, Terebratula punctata, &c. 



Mineral Character. — At the outcrop, the iron-bed presents a rich ferruginous aspect ; 

 but when followed to some depth below the surface, the original colour is found to be 

 olive-green, and under the magnifying glass the stone appears oolitic. In this state 

 the ore is probably a carbonate and silicate of iron — the latter imparting a green 

 tinge. When exposed, it passes into a hydrated peroxide of iron. The remaining 

 constituents are carbonate of lime, 10 per cent. ; silica, 12 per cent. ; alumina, 7'8 per 

 cent. Phosphoric acid is only present in minute quantity, viz. 0'55 per cent. The 

 chief market for the ore is expected to be South Wales*. 



Thickness of the Formations below the Great Oolite at Slonesjiehl. 



For the purpose of ascertaining the depth of the iron-bed below the Stonesfield 

 slate, the Duke of Marlborough directed that one of the slate pits should be continued 

 downwards till the ore was reached. This has not been accomplished ; for on reach- 

 ing at a depth of 120 feet the Upper Lias Clay, the water flowed in so plentifully that 

 the men were drowned out. With the assistance of numerous sections near Fawler, 

 the deficiency in the series may be supplied ; and the following are the results : — 



Succession of Strata at Stonesfield. 



feet. 

 Great Oolite. 1. Upper Zone. — White limestone, resting on calcareous shales 



and marls (total thickness about) 100 



2. Lower Zone. — Sandy shales, flags, and shelly oolite, with a band of 



" Stonesfield slate " at 10 feet from the top '. 80 



Inferior Oolite. Upper Ragstone (zone of Ammonites Parkinsoni). — Large- 

 grained, rubbly oolite, very fossiliferous, with Trigonia costata, Lima 



gibbosa, Terebratula globata, Clypeus Plotii 30 



Upper Lias Clay. — Blue laminated clay 6 



Marlstone. 1. Iron-bed. — Massive ferruginous rock, with Rhynchonella tetra- 

 hedra, &c 10-15 



2. Sands, with iron concretions atop 15 



Lower Lias Clay. — Thickness unknown. 



Comparing the development of these formations with that which they attain in 

 Gloucestershire, the author showed that they all tended to decrease in thickness when 

 traced from the north-west towards the south-east of England, and contended that 

 these facts bore out the theory which he had on previous occasions endeavoured to 

 demonstrate, that all the secondary rocks of England undergo attenuation towards 

 the south-east. The following comparison had been arrived at from carefully mea- 

 sured sections : — 



Comparative Sections. 



Gloucestershire. Oxfordshire. 



Maximum thickness. Minimum thickness. 



feet. feet. 



Fuller's Earth 40 



Inferior Oolite 264 5 





 6 



Marlstone 250 25 



Lower Lias 600 (nearly) ? 



tt™™,. t;™ /Sands... 20-50 

 Upper Lias j ghale> __ 38Q 



The author considers it probable that under Oxford the Great Oolite is separated 



* As this ore extends under the property of the Duke of Marlborough, theauthor has 

 named it the " Blenheim iron-ore ;" and for fuller details refers to his memoir, "The Geo- 

 logy of the Country round Woodstock," Mem. Geol. Survey, 1857. 



