New Oolitic Strata in Oxfordshire. 707 



Chipping-Norton Limestone by a bed with vertical markings and a 

 black clay-band, indicative of much ' inter-waste ' of these and other 

 beds, are described. They are shown to be similar to the Lincoln- 

 shire (Ponton) strata described by Morris, Judd, and Woodward. 

 A new term is proposed for these beds, which are characterized by 

 the presence of the shell Necera, from the iVna-Harls above the 

 black clays to a higher series of black-and-green clays underlying 

 the Stonesfield Slate. These beds and the Chipping- Norton Lime- 

 stones are classed with the sub-Bathonian. The beds equivalent 

 to those of Oxfordshire have, in Lincolnshire and Northampton- 

 shire, been known in part as Upper Estuarine. In the !^0 feet of 

 Oxfordshire strata there appears to be represented the 150 feet of 

 the Lincolnshire Limestone and the Upper Estuarine of the north- 

 eastern counties. The author expresses the hope that his work 

 may help towards the discrimination of the two kinds of deposit 

 known as Lincolnshire Limestones, inasmuch as the fossils charac- 

 terizing each local (Oxfordshire) stratum have been collected from 

 the beds in situ. Lists of fossils are given. 



4. 'The Causes of Variegation in Keuper Marl and in other 

 Calcareous Rocks.' By Gerald Tattersall Moody, D.Sc, E.C.S. 



Analyses of a large number of specimens of Keuper Marl bring 

 to light the fact that the red portion of a variegated rock contains 

 a considerably-higher percentage of iron and lower percentages of 

 calcium-carbonate and magnesium-carbonate than the green portion. 

 This is in agreement with earlier observations that red strata are 

 usually less calcareous than adjacent green strata ; but the author 

 is unable to confirm the hypothesis advanced by Maw, that the 

 lighter-coloured bands in variegated rocks are produced by bleaching 

 or discoloration of red rocks through addition from extraneous 

 sources of lime and magnesia. On the contrary, it is found that 

 the removal of iron existing as ferric oxide from a homogeneous 

 rock-mass is inhibited, if calcium-carbonate, or magnesium-car- 

 bonate, or both of these substances be present. When, however, a 

 chalybeate water (ferrous bicarbonate-solution) permeates a rock 

 containing magnesium-carbonate or calcium-carbonate, iron is pre- 

 cipitated as ferrous carbonate, and an equivalent weight of mag- 

 nesium or calcium passes into solution. Subsequent access of air 

 oxidizes the ferrous carbonate, and red or yellow ferric oxide is 

 produced. The author finds that when a green marl is subjected to 

 the action of chalybeate water in the manner indicated, it is readily 

 converted into a material closely approximating, both in appearance 

 and in composition, to the natural red marl of the same rock-mass. 



The author concludes that the variegation of the Keuper Marls 

 and of other calc* reous rocks has been brought about by the 

 percolation of chalybeate water through the light-coloured mass, 

 the more porous parts of which have in consequence become stained 

 with ferric oxide, while the harder and more crystalline parts, 

 being non-porous, have remained unchanged. The uniformity in 

 distribution of ferric oxide in some red rocks, such as the New 

 Red Sandstone, suggests that the iron contained in them has 

 probably been derived from chalybeate water in a similar manner. 



