THE GEOLOGY OF BARBADOS. 



189 



finely-divided state. The accompanying analyses (p. 188) illustrate 

 the variations in their composition ; analyses of radio] arian oozes 

 from stations 265 and 271 of the ' Challenger ' Expedition are given 

 for comparison.^ 



Modern radiolarian oozes are generally of a reddish colour ; but 

 Dr. Murray informs us that some of them become grey when dry, 

 and the subsequent leaching out of the oxides of iron and manganese 

 by percolating water might decolourize them altogether. 



(d) The Red and Mottled Argillaceous Earths. — These beds dijffer 

 from the rest of the Oceanic Deposits, being somewhat light earths 

 or clays having a peculiarly greasy feel, ranging in colour from a 

 dark chocolate-red through various shades of red and pink to yellow 

 and greyish white, sometimes being mottled. Physically they have 

 a closer resemblance to ' fuller's earth ' than to true clays. The 

 colours appear to be due to the state of combination and hydration 

 of the iron peroxide present and to the manganese peroxide which 

 they all contain, partly in the form of coatings upon their joint- 

 planes or of minute spherules. They contain comparatively small 

 amounts of colloid "silica in the form of sponge-spicules and an occa- 

 sional radiolarian, but are in all cases free from calcareous organisms. 

 Out of all the numerous samples examined calcium carbonate or lime 

 was only determined in one, and there amounted to less than 1 per 

 cent, of lime. The following are the compositions of some of the most 

 characteristic samples examined : — 



Loss on ignition 



Quartz 



Colloid silica 



Combined siUca (by difference) 



Iron peroxide 



Alumina 



Manganese peroxide 



Lime 



Magnesia 



Potash 



Soda 













^_:^ 





-^ 



1 



>^, 



>. 





^% 



c'^'? 



^ ^ 



^^ 



a 



^.f 



si: 





?|1 





^t 



er 



O .rH 



^95 





C^ 



§1 



3 3 





S ^ '^ 





o ^ — 



o •— ' 



O -—' 



o 



6 



^ 



^ 



^ 



^ 



8-55 



7-46 



6-41 



7-10 



4-72 



7-42 



•41 



•23 



-52 



-76 



•73 



1-98 



4-98 



3-87 



4-14 



4-85 



5-76 



5^57 



47-65 



46-17 



43-38 



51-70 



54-50 



48-43 



4-86 



4-77 



8-32 



2-84 



6-95 



5-09 



25-20 



31-54 



31-56 



25-48 



21-03 



26-99 



3-05 



2-69 



1-77 



2-71 



1-24 



2-73 



trace 



trace 









trace 



2-57 



141 



1-44 



2-68 



2-62 



•98 



•18 



■10 



•17 



•10 



-50 



•07 



2-55 



1-76 



2-29 



1-78 



1-95 



•74 



1 0000 



10000 



100-00 



100-00 



10000 



100-00 



We have been favoured by Dr. John Murray with the analyses of 



the samples of red clay obtained by the ' Challenger ' Expedition ; 



they will be found in extenso on page 198 of his report on the 



* Deep-sea Deposits/ and we find that the majority of them appa- 



1 ' Challenger ' Reports, ' Deep-sea Deposits,' pp. 435, 433. 



