ON THE GEOLOGY OF BAEBADOS. 



193 



from Melvin's Hill) contained considerable proportions of tlie oxides 

 of manganese, of which only traces were present in the mudstoue 

 from Mount Hillaby and in the May Dust. We examined many years 

 ago a sample of May Dust which contained oxides of manganese in 

 considerable quantity, a fact which was noted by Sir Humphry 

 Davy, who examined some of it soon after its falling. 



The older layers of volcanic materials contain much less lime than 

 do the Mount Hillaby and May Dust samples. 



The occurrence of these layers of volcanic sands and muds in the 

 Oceanic Deposits, the general resemblances in composition between 

 them and the argillaceous earths, and the fact that minute fragments 

 of pumiceous minerals are scattered throughout the beds, point 

 strongly to the conclusion that the clay present in the Oceanic 

 Deposits has been derived from the finest portions of the volcanic 

 materials which fell from time to time upon the surface of the area 

 in which the deposits were forming. 



§ 4. Oeganic Remains pound iisr the Eocks. 



With the exception of radiolaria, which abound in the siliceous 

 earths, and of foraminifera, which are equally abundant in some of 

 the calcareous rocks, fossils are very rare in the Oceanic Deposits of 

 Barbados. The discovery of the Cystechinus described by Mr. Gregory 

 shows, however, that larger organisms were not entirely absent ; ^ 

 but the very paucity of such remains is another point of resemblance 

 between these deposits and the modern abyssal oozes. 



It is, of course, only from a comparison of the constituent and 

 embedded organisms with their living congeners that conclusions 

 can be drawn respecting the age of the deposits and the depth of 

 water in which they were accumulated. In considering the bearing 

 of the fossils on these points, it will be convenient to deal separately 

 with the contents of (1) the siliceous earths, (2) the calcareous 

 earths. 



(1) Fossils from the Siliceous Earths. — The radiolaria from these 

 deposits have long been known, and it would serve no useful purpose 

 to give a list of them here ; but we may note an important obser- 

 vation by Prof. Haeckel to the eJffect that the fossil radiolaria of 

 Barbados are most nearly allied to those which occur in the deepest 

 parts of modern oceans.^ ]^ow radiolarian oozes are found in the 

 Pacific and Indian Oceans between depths of 2000 and over 4000 

 fathoms, and it is a fact significant of the physical changes which 

 have taken place since the formation of radiolarian ooze in the 

 Caribbean region that no such ooze has been found in the modern 

 Atlantic ; that is to say, no deposit which contains more than 50 

 per cent, of radiolarian remains. 



Haeckel also compared the species of radiolaria found in the 



^ Another echinoid {Archcsopneustes, Greg.), with some small turbinate corals, 

 and some other fossils occur in the limestone which caps Bissex Hill, but we 

 do not regard this as, sti-ictly speaking, part of the Oceanic Series (see § 6). 



- ' Challenger ' Reports, vol. xviii. part i. p. clxxv. 



