Analysis of Red Chalk and Bed Clay. 333 



Although the above numbers clearly indicate a substance which 

 may be fairly designated "a silicate of red oxide of iron and 

 alumina," like the "red clay" of Professor Wyville Thomson, 1 it 

 would be idle now to speculate as to the probable correspondence, 

 in the minuter details of their composition, of the red chalk residue 

 with the red clay of the deep Atlantic and Southern Sea. Still it 

 may be profitable to allude to two or three points which are likely 

 to throw light upon the relationship of the white, grey, and red 

 chalk with the globigerina, the grey and the red ooze, respectively. 

 First, analysis seems to show that the removal, in different degrees, 

 of calcareous matter, however effected, has been the main cause of 

 the differences of such formations. Secondly, it would appear that, 

 although manganese dioxide is present in granules and nodules in 

 the red oceanic clay and in the coarser particles of the red chalk, it is 

 absent alike from the finely-divided substance of the former and the 

 similar red residual slime of the latter. And, thirdly, the suggested 

 relation beetween both these red matters and the mineral known as 

 glauconite receives an unexpected light through the detection of 

 sensible quantities of magnesia and potash in the red chalk residue ; 

 for the latter base is an invariable constituent, and the former an 

 usual one of this species. 



The complex and rather variable silicate which, from its grey- 

 green hue, has received the name of glauconite, is known both in 

 ancient and recent formations of greensand. The casts of animal 

 forms which constitute the glauconitic grains of Cretaceous Greensand 

 strata are paralleled by similar remains in the recent greensands of 

 the Australian seas, and of those of the Agulhas current investigated 

 by the scientific staff of H.M.S. Challenger. But the problem of the 

 formation of recent greensand, or rather of glauconitic matter, at 

 moderate depths, and of the related red clay at very great depths, 

 is not yet solved. It is by no means necessary to suppose that 

 glauconite was always first formed, and that it yielded the red clay 

 in question by oxidation and partial solution, just in the same way 

 that kaolin or white clay has been produced from felspar. This has 

 probably happened in some instances ; but it may be assumed, on 

 the other hand, that the same constituents have yielded one or other 

 of these two products, in accordance with differences in the dissolved 

 gases and salts of the ocean and in the nature of its prevalent animal 

 and vegetable forms. 



One step towards the discoveiy of an answer to the problem now 

 under discussion might be furnished by a careful study of the action, 

 under pressure, of water holding oxygen and carbon dioxide in 

 solution, upon powdered glauconite. But we really stand in need 

 of more information as to this species itself, for the composition of 

 the numerous minerals included under this name is somewhat ill- 

 defined. Still we may conclude that it contains, as essential con- 

 stituents, silica to the extent of 50 per cent. ; a variable amount of 

 alumina; much iron in the ferrous, as well as in the ferric condition; 

 several per cents of potash ; a little magnesia ; and, finally, about 

 1 Proc. Eoy. Soc, vol. xxiii. pp. 39 and 45. 



