200 ME. JUKES-BROWNE AND PEOF. HAEEISON 



deDce for a very late Tertiary date, either Pleistocene or late 

 Pliocene time. 



The occurrence of the genus Cystechinus in the siliceous earths is 

 confirmatory of this conclusion. As that genus is known only in 

 a living condition, it might be thought to favour a very recent age, 

 but inasmuch as its representatives are entirely confined to deep 

 vi^ater it may be inferred that the genus is a Tertiary form which, 

 like many of its associates, has lived on in the ocean depths. It is 

 therefore just as likely to occur in deep-sea deposits of Pliocene as 

 of Pleistocene age. 



We may conclude then that the Oceanic Deposits of Barbados 

 were most probably formed during the period which we call Pliocene ; 

 and it is possible that, with the still later deep-water deposits, they 

 cover not only the whole of Pliocene time, but so much of the post- 

 Pliocene as elapsed before the rising island reached the level at 

 which reef corals could build. 



Next, with regard to the depth of water which is indicated by the 

 fossil organisms. In an area which has certainly experienced a 

 profound subsidence, followed by an equally great upheaval, the 

 depth of the sea during the accumulation of oceanic oozes may 

 have varied very much, and the great variety of deposits exhibited 

 by the Oceanic Series of Barbados suggests a concomitant variation 

 in depth. It is true that the accumulation of red clay does take 

 place in some areas at the same depths as those in which radiolarian 

 ooze or foraminiferal ooze is being formed elsewhere, and conse- 

 quently the change from one kind of deposit to another must depend 

 on other conditions besides the single element of depth. Still, we 

 may be prepared to find that the contents of the successive deposits 

 do indicate different depths of water. 



With respect to the calcareous earths the evidence of the foramini- 

 fera does not seem to be very clear or definite. Of the samples 

 examined by Dr. Brady and mentioned in his list three came from 

 the basal beds, while the other two came from higher horizons. 

 There are 25 species in the latter which were not found in the 

 former, but the fauna of the lower beds is not so uniform as to show 

 that these species are not likely to occur in it, for Canefield alone 

 yielded 16 species which were not found at the other two localities, 

 while some of these 16 also occurred in the higher beds. It is clear 

 that, as Dr. Brady remarks, fuller lists are required, and all that 

 can be said is that the fauna of the beds at both horizons is consistent 

 with a depth of from 500 to 1000 fathoms. 



Of the Glohigerina-rock which occurs on Bissex Hill and belongs 

 to the higher calcareous horizon Dr. Brady speaks more confidently 

 as indicating a depth of about 1000 fathoms, and certainly formed 

 in open ocean far away from land. It is noteworthy too that of the 

 salient species pointed out by him the four species whose range is 

 best known, viz. Miliolina venusta, Oassidulina suhglohosa, Polymor- 

 phina angusta, and Rotalia Soldanii, are all most abundant in depths 

 of more than 1000 fathoms. 



