496 ECONOMICAL QUESTIONS. CHAP. 



the abundant ' yield ' of Northamptonshire. The oldest and most 

 extensive has been explored in the marlstone, below thin upper 

 lias shale, in the Vale of the Evenlode at Fawler, near Charlbury, 

 on the property of the Duke of Marlborough. It corresponds in 

 g eological position with the famous and valuable bands in the hills 

 above Middlesborough and Guisborough in Yorkshire. 



This stone, opened since the notices on p. 115 were written in 

 several places in the Vale of Cherwell, as Claydon, Adderbury, 

 King's Sutton, Aynhoe, and Steeple-Aston, has been found rich 

 enough in iron to be worthy of the attention of the great works 

 in Staffordshire and South Wales. In many pretty large areas, 

 especially on the western side of the vale, it lies near the surface 

 and can be wrought by open cutting very economically. In some 

 tracts which are thus situated the stone, having been long exposed 

 to atmospheric influences, is broken up horizontally into thin beds, 

 and the upper parts have lost portions of the soluble carbonate ; 

 but in other places, where a thin clay bed of the upper lias covers 

 the rock, this does not happen. There the whole mass of the 

 ' marlstone' with its several bands of shells is solid, and all rich 

 enough for the furnace. 



The most important work at present in hand, at Adderbury, 

 shews an open front of some hundreds of yards, only inferior to the 

 great escarpments of Esten-Nab and Upleatham in Yorkshire. 

 The rock is eleven feet in thickness, partly blue, or green within 

 the large blocks, often compactly ferruginous in the joints, traversed 

 by brown veins, and in substance finely oolitic. No part appears 

 to be magnetic. Shell bands run irregularly through it, mostly 

 formed of Rhynchonella tetraedra, with sparry interiors. Vertical 

 joints filled with clay, running north and south, divide the beds, 

 and between these the rock has the appearance of having been 

 tilted, so as to make frequent parallel waves above a foot high. 

 These appearances are observed under a clay covering with a thin 

 course of stone containing more than elsewhere Ammonites com- 

 munis. In other parts of this extensive work the same bed is less 

 solid, but equally rich. Where most productive the yield may be 

 reckoned at about 30,000 tons to the acre ; every three tons of the 

 best samples producing one ton of iron. The poorer parts, on 

 account of the carbonate of lime which they contain, are useful 

 in the furnace as 'limestone.' Below the iron-stone is a grey 



