212 MK. JUKES-BROWNE AND PEOF. HAREISON 



100 feet are cut through in the vaUej south of the bay, exposures 

 occurring at intervals. In the cliff at Pico Teneriffe about 50 feet 

 are seen, the beds dipping at a low angle to the N^.IST.E., and 

 underlying a plateau of coral-rock, the base of which gradually 

 slopes northward till it reaches the sea in Gay's Cove. 



Bisseoc Hill. — The deposits which form this outlier present some 

 iuteresting local peculiarities. A good section is afforded by the 

 cutting for the road that is carried up the southern face of the 

 hill. On this the usual chalky basement-beds occur at a level of 

 765 feet, passing up into greyish-buff calcareo-siliceous beds in 

 alternating hard and soft courses. The beds dip into the hill at an 

 angle of 5° or 6° ; and the brown gritty layer, which occurs about 

 80 feet up in the series, crosses the roadway about 30 feet vertically 

 above the level of the base. Above this, white siliceous beds con- 

 tinue for some distance, but about 140 feet (vertically) above the 

 base a hard bluish-grey limestone more than a foot thick occurs in 

 the bank and weathers out in large blocks, some of which have 

 been carried up to the hill-top and used both for building and for 

 road-metal. Above this again siliceous earths can be seen for about 

 10 feet ; but the higher part of the hill is covered with a yellowish 

 granular marl, with layers and concretionary lumps of harder 

 yellowish granular marlstone, which prove to consist entirely of 

 foraminifera and chiefly of Glohigerinoe loosely compacted by a 

 calcareous cement. 



The highest knoll or summit/ on which the flagstaff is placed, 

 consists of firm foraminiferal marl, or what might be called a soft 

 marlstone, and the surface of this is covered with blocks of hard 

 yellowish fossiliferous limestone. These blocks are of aU lengths 

 up to about 2| feet, and as they were found to consist chiefly of 

 foraminifera we supposed that they had been originally embedded 

 in foraminiferal marl of a similar character to that which forms 

 the base of the knoU. 



Subsequently, however, we felt some doubt about this point, and 

 asked Mr. G. F. Franks, F.G.S., to obtain further information for 

 us. This he kindly did, sending us a fresh set of specimens, and 

 in one of these we detected what appeared to be fragments or 

 pebbles of a previously consolidated rock. This specimen was sent 

 to Mr. W. Hill, F.G.S., who reports that our surmise is correct, 

 the included fragments consisting of an indurated foraminiferal 

 marl or chalk, like those which occur so generally in the Oceanic 

 Series. 



The mass of the rock consists of the tests of foraminifera em- 

 bedded in crystallinp calcite, and conseque;ntly when a small slice 

 is seen under the microscope it much resembles the Globigerina 

 marlstone above mentioned, but there is a greater variety of 

 foraminifera, and fragments of the plates and spines of echinoderms 

 are seen here and there. These differences are more conspicuous 

 in a hand-specimen, the shining surfaces of the broken echinoid 



^ [The remainder of this descripLion of Bissex Hill has been re- written.— 

 Feb. 16th, 1892.] 



