186 



MR. JUKES-BROWNE AND PROF. HARRISON 



The analyses of oceanic foraminiferal oozes to whicli we have 

 access are those on pages 369-381 of the second volume of ^ The 

 Yoyage of the ' Challenger.' ' These, rearranged from the figures 

 there given so as to he more easily comparable with ours, are as 

 follows : — 



Number of sample 

 Depth in fathoms . 



on ignition 



Clay, quartz, &c 



Colloid silica 



Iron peroxide and alumina 



Calcium phosphate 



Calcium sulphate 



Calcium carbonate , 



Magnesium carbonate 



1 



2 



11 



12 



19 



1890 



1945 



1950 



2325 



1420 



7-91 



5-02 



4-58 



4-17 



3-80 



1902 



12-08 



4-60 



8-33 



3-45 



1210 



9-08 



4-60 



9-16 



4-14 



9-21 



7-41 



3-33 



6-25 



4-42 



trace 



trace 



1-12 



trace 



2-41 



•44 



•69 



1-20 



1-91 



•41 



50-00 



64-55 



79-17 



67-60 



80-69 



1-32 



117 



1-40 



2-58 



•68 



100-00 



100-00 



100-00 



100-00 



10000 



The variations in composition in these Glohigerina-oozes are 

 similar to those in the Barbados foraminiferal beds, and whilst 

 there is a general resemblance in composition between them there 

 are certain well-marked differences. These are in the ' Challenger' 

 samples the uniformly larger " loss on ignition," the presence of 

 much larger quantities of calcium sulphate and of iron peroxide 

 and alumina, and the absence of manganese peroxide and of lime 

 and magnesia in the form of hydrous silicates. As only small quan- 

 tities of the oozes were available for analysis, it is possible that the 

 latter points may not represent real but merely apparent differences 

 in composition, resulting from the methods of analysis used. The 

 differences in " loss on ignition " and in calcium sulphate are what 

 we should expect to be the result of the natural changes incidental to 

 the exposure of the Barbados rocks to the action of water and air, 

 by the removal of the more easily soluble constituents and the oxi- 

 dation of the organic matter. 



(b) The Foraminiferal-radiolarian Beds. — These occur above the 

 purely foraminiferal rocks at the base of the Oceanic Beds, and also 

 below the upper chalks. They contain large proportions of calcium 

 carbonate, occasionally as much as some of the purely foraminiferal 

 rocks, from which they are distinguished by having a large propor- 

 tion of their colloid silica in the form of definite siliceous organisms, 

 such as radiolaria, spouge-spicules, &c. There is a general resem- 

 blance in chemical composition between these beds and the more 

 siliceous bands of the purely foraminiferal beds. 



We have not access to analyses of modern oozes comparable with 

 this group, but we may quote the following remarks by Prof. 

 Haeckel as showing that such deposits undoubtedly exist among 

 recent oceanic oozes : — " Mixed radiolarian ooze is the name given 

 to those deposits in which the radiolaria exceed any of the other 

 organic constituents, although they do not make up half the total 



