Vol. 55-] 



OT? THE OCEANIC DEPOSITS OF TEINIDAD. 



185 



For comparison with the foregoing analyses, it will be useful to 

 state the average composition of the corresponding beds in Barbados ; 

 this is as follows : — 





Glohigerina- 

 chalks. 



Passage- 

 beds. 



Kadiolarian 

 beds. 



/lioss on ignition 



2-71 



70-40 



•37 



10-52 



2-89 



•48 



•74 



•92 



10-28 

 •22 

 •26 

 •21 



2-64 



60-49 



•47 



18-05 



3-09 



-93 



1-10 



•72 



11-80 



•29 



•19 



•23 



4-38 



10-65 



•41 



46-70 



609 



•18 



2-20 



1-09 



19-31 



•37 



•95 



1^07 



1 Calcium carbonate 



A..-{ Calcium phosphate 



1 Magnesium carbonate 



I Colloid silica 



l' Iron peroxide and alumina 

 1 Manganese peroxide 



-Q ! l/ime 



j Magnesia .. 



1 Clav and silicates . . . 



I Alkalies and loss 



C. Quartz 



D. Calcium sulphate 





100-00 



100-00 



10000 



The resemblances and differences between the two series will be 

 more aj^parent, if the two sets of analyses are summarized as 



follows : — 





Glohiger 



"wa-beds. 



Passage-beds. 



Radiolarian beds. 



Trin. 



Barb. 



Trin. 



Barb. 



Trin. 



Barb. 



Organic constituents 

 Earthy constituents 

 Quartz 



47^32 



45-89 



602 



•77 



84-00 



15-53 



•26 



•21 



63-15 



33-29 



3-39 



•17 



81-65 



17-93 



•19 



•23 



75-36 

 21-70 



2-76 

 •18 



68-14 



29-84 



•95 



1-07 



Adherent salts 



10000 



100-00 



100-00 



100-00 



100-00 



100-00 



From the foregoing table it is seen that considerable differences 

 exist between the Oceanic deposits of Trinidad and Barbados, and 

 this is more particularly the case with the lower members of the 

 series. The higher proportions of quartz and of argillaceous matter 

 in the Globigerina-ma,rl8 of Trinidad point to their having been 

 deposited rather nearer land than those of Barbados. The calcareo- 

 siliceous beds show the same differences, but with regard to the 

 purer radiolarian earths the case seems at first sight otherwise, 

 for, though the proportion of quartz is higher in Trinidad, that 



