ON- THE GEOLOGY OE BARBADOS. 213 



plates and spines giving it a different aspect, while in some of the 

 blocks casts of turbinate corals are abundant.^ 



It would appear, therefore, that these blocks are the broken 

 remnants of a stratum which once capped the hill, and that the 

 rock is of later date than any part of the Oceanic Series. The 

 limestone blocks are partially embedded in a loose crumbling marl, 

 but a sample of this received from Mr. Franks proves to be a 

 material quite different from that in situ below and similar to that 

 of the limestone, for it contains a variety of organic fragments such 

 as small joints of Pentacrinus, echinoderm spines, and broken 

 (? pteropod) shells, all more or less worn and rolled, while Glohi- 

 gerince, though abundant, do not make up more than 20 or 25 per 

 cent, of the mass. 



This crumbling marl may have resulted from the disintegration 

 of the limestone, but, however this may be, it certainly is not a 

 true Oceanic Deposit. We regard it and the associated limestone 

 as equivalents of the foraminiferal muds hereafter described (p. 215), 

 which occur at several localities between the Oceanic Series and the 

 coral-rocks ; for if this capping of Bissex Hill does not belong to the 

 Oceanic Marls on which it rests it must he unconformable to them, 

 all the red-earth group and the volcanic muds of Mount Hillaby 

 being absent on Bissex Hill. 



The summit of the hill is 190 feet above the point where the 

 base of the Oceanic Series occurs, and about 700 yards in horizontal 

 distance from it ; in this distance a dip of 5° would bring in a 

 thickness of about 60 feet which, added to the 190 feet of vertical 

 difference, gives a total thickness of 250 feet for the portion of the 

 series here preserved. 



Mr. Pranks also writes to us that he has found the hard grey 

 siliceous limestone exposed in two places, by the road which runs 

 along the north-eastern slope of the hill towards Bissex Estate 

 House. Here there are several layers of it alternating with greyish 

 white earth, and near one exposure a bed of fine, dark grey sand- 

 stone appeared, probably the representative of the pumiceous sand 

 at Chimborazo. 



On the extreme northern spur of Bissex Hill, half a mile beyond 

 the Estate House, another limestone occurs, apparently at the very 

 base of the Oceanic Series. This is a hard, compact blue limestone, 

 smoother and bluer than the upper one, and forms a continuous bed 

 some 3 or 4 feet thick, which weathers to a yellowish buff where 

 exposed to the air. This bed can be traced for a little distance, 

 dipping N.E. by N., and it appears to rest on the Scotland rocks. 



Small outliers of siliceous earth occur at Cambridge to the E. 

 and near Hopewell to the N.W., but do not present any features of 

 special interest. 



Comparing the sections we have now described with one another, 



^ We understand from Mr. Franks that it was from this limestone that the 

 echinoderm described by Mr. Grvegory as Archtsopneicstes abrupt us was obtained. 

 The Scalaria figured by Sir R. Schomburgk probably came from the same 

 rock. 



