174 MR. JUKES-BEOWNE ANB PBOF. HAERISON 



(c) Siliceo-calcareous Earths. 



Castle Grant, lowest beds, No, 1 . 



do. do. No. 2. 



do. upper beds. 



Joe's Kiver, low level. 



Conset Bay gully, near the base, hard chalky bed. 

 Conset Bay gully, higher beds. 

 Chimborazo, 3 feet under red clay. 



do. middle bed in road-cutting. 



Mount Misery. 

 Mount Ilillaby, 20 feet from the top of the southern peak. 



In these specimens entire siliceous organisms or their comminuted 

 remains preponderate, so far as one can judge by the eye. There 

 is, however, a considerable variation in the amount of perfect 

 skeletons which can be recognized. This is due in some degree to a 

 difference in the character of the deposit. Thus in the Castle Grant 

 (lowest), Mount Misery, and Joe's River samples few entire radio- 

 larian skeletons can be noticed, but examination of the finer material 

 shows it to be chiefly radiolarian debris, with a small amount of 

 calcareous matter and fine inorganic particles. In the rest, some of 

 which are rather more calcareous, entire radiolarians are abundant 

 and foraminiferal tests few and far between, sponge-spicules occur 

 commonly, and in all there are angular mineral-grains. 



(d) Siliceous Earths. 

 Loam field inlier. 

 Burnt Hill, Conset Bay. 

 Springfield. 



Chimborazo (brown band), 

 do. (No. 1). 



These are the earths from which the well-known radiolaria of 

 Barbados are extracted. They consist entirely of radiolarians and 

 sponge-spicules with a few diatoms ; there are no recognizable 

 calcareous organisms, but a few small calcareous particles can some- 

 times be detected. The matrix is a felted mass of interlacing 

 fragments of radiolaria and sponge-spicules, and is therefore very 

 different from that of the more calcareous earths.^ 



The rocks which are included in group 1 {a, 6, c, and d) do not 

 seem to have undergone much change since their deposition, beyond 

 a certain degree of consolidation. This is especially the case with 

 the more purely calcareous (chalky) and the purely siliceous earths. 

 The changes which have taken place are most evident in those 

 which contain both calcareous and siliceous organisms. 



When thin sections of these mixed deposits are compared, it is 

 seen that the radiolarian form becomes most easily lost. Radio- 

 larians are not readily seen in chalky sediments, even if perfect, 

 and when the skeleton becomes filled with calcareous material all 



^ [This felted structure is described as conspicuous in deeper layers of the 

 radiolarian ooze brought up from 4475 fathoms in the North Pacific ; see 

 ' Report on the Deep-sea Deposits,' Chall. Exp. p. 175. In the interstices of 

 this felted matrix may be seen aggregations of minute granular particles 

 which resemble those shown in plate xxvii., fig. 5, of the same Report. — 

 A. J. J.-B., Feb. Srd, 1892.] 



