ON THE GEOLOGY OE BARBADOS. 201 



The minute, calcareous, stellate particles which occur so abun- 

 dantly in the more chalky beds, and which appear to be of organic 

 origin (see p. 178), confirm the evidence of the foraminifera, but do 

 not afford any more precise indication of the depth of water, inas- 

 much as they occur in modern Glohigerina-ooze at all depths from 

 about 600 to 2000 fathoms. 



With respect to the siliceous earths we have Haeckel's testimony 

 that the radiolaria suggest depths comparable to the deepest parts of 

 the modern oceans (3000-4000 fathoms) ; and we have the evidence 

 of the Cystechinus and of the diatom Ethmodiscus, both of which 

 are quite compatible with a depth of more than 2000 fathoms. 



While, therefore, it is at present impossible to say at what depth 

 the basal chalky earths were formed, we may safely assume that 

 the water became gradually deeper owing to continued subsidence, 

 till during the formation of the purely -siliceous radiolarian earths 

 its depth was between 2000 and 3000 fathoms ; that the movement 

 was then reversed, and upheaval brought the sea-floor to within 

 1000 fathoms of the surface during the formation of the upper cal- 

 careous beds. The red clays can hardly have been accumulated in 

 a less depth than 2000 fathoms, and it is possible therefore that 

 they indicate a second subsidence. Finally we have the topmost 

 beds of Mount Hillab)'', which may have been accumulated in almost 

 any depth, but still at a distance from land. Such are the conclu- 

 sions which seem fairly deducible from the evidence. 



§ 5. Steatigeaphical Desceiption oe the Oceanic Deposits. 



(a) Areas of Exposure.- — The chief physical feature of Bar- 

 bados is the escarpment of coral-rock which was described in the 

 first part of this memoir. This embraces and forms the boundary of 

 the area known as the Scotland district, and it is within this district 

 and its prolongation along the coast to the south-east that the chief 

 exposures of the two older rock-groups are to be found. 



At each end of the area above indicated (see Map, facing page 

 202) the Oceanic Beds are found at the sea-level ; toward the centre 

 of the island, between Mount Chimborazo and Mount Hillaby, their 

 base rises to between 800 and 900 feet above the sea. 



At the southern end of the narrow strip of ground which lies 

 between the sea and the high plateaux of coral-rock in the parish 

 of St. John's, the lower platforms of coral-rock terminate in a low 

 semicircular escarpment. Beneath this are slopes formed by the 

 outcrop of the white earths of the Oceanic Series, and these slopes 

 enclose a valley which opens north-eastward into Conset Bay and 

 along which the Scotland Beds are exposed. 



Prom Codrington and Conset Bay the Oceanic Deposits occupy 

 most of the ground between the coast and the great escarpment, as 

 far as Congor Rock and Newcastle estate ; a powerful fault then 

 brings up the Scotland Series and throws back the base of the white 

 earths to a height of about 200 feet above the sea, where they form 

 a narrow strip of ground beneath the lowest terrace of coral-rock. 



p2 



