Ill EXPEDITION OF THE "CHALLENGER" 99 



Buchanan to the action of weak acid ; and he found that there 

 remained after the carbonate of lime had been removed, about 

 1 per cent, of a reddish mud, consisting of silica, alumina, and 

 the red oxide of iron. This experiment has been frequently 

 repeated with different samples of Cflobigerina ooze, and always 

 with the result that a small proportion of a red sediment re- 

 mains, which possesses all the characters of the red clay." 

 # * * * 



" It seems evident from the observations here recorded, that 

 clay, which we have hitherto looked upon as essentially the 

 product of the disintegration of older rocks, may be, under 

 certain circumstances, an organic formation like chalk ; that, as 

 a matter of fact, an area on the surface of the globe, which we 

 have shown to be of vast extent, although we are still far from 

 having ascertained its limits, is being covered by such a deposit 

 at the present day. 



" It is impossible to avoid associating such a formation with 

 the fine, smooth, homogeneous clays and schists, poor in fossils, 

 but showing worm-tubes and tracks, and bunches of doubtful 

 branching things, such as Oldhamia, silicious sponges, and 

 thin-shelled peculiar shrimps. Such formations, more or less 

 metamorphosed, are very familiar, especially to the student of 

 palaeozoic geology, and they often attain a vast thickness. One 

 is inclined, from the great resemblance between them in com- 

 position and in the general character of the included fauna, to 

 suspect that these may be organic formations, like the modern 

 red clay of the Atlantic and Southern Sea, accumulations of the 

 insoluble ashes of shelled creatures. 



"The dredging in the red clay on the 13th of March was 

 unusually rich. The bag contained examples, those with cal- 

 careous shells rather stunted, of most of the characteristic deep- 

 water groups of the Southern Sea, including Umbellularia, 

 Euplectella, Pterocrinus, Brisinga, Ophioglypha, Pourtalcsia, 

 and one or two Mollusca. This is, however, very rarely the 

 case. Generally the red clay is barren, or contains only a very 

 small number of forms. 



It must be admitted that it is very difficult, at 



