230 MR. JT7KES-BR0WNE A5D PEOF. HARRISON 



how largo and interesting a field of enquiry still remains in this 

 region. 



(a) Guadalupe. — This island is divided into two dissimilar por- 

 tions by deep inlets ; the western peninsula is entirely volcanic, but 

 the eastern, which goes by the name of Grand' Terrc, is entirely 

 composed of raised coral-reefs and their associated calcareous de- 

 ])Osits. It is described as presenting " an undulating elevated 

 alluvial soil, above which rise a number of small steep round hills, 

 or mamelons, to a height of perhaps not more than 1300 feet. These 

 hills are composed of fossiliferous limestone, full of shells and corals 

 of the same species as are still found alive in the neighbouring 

 waters.* ''. A few species of corals from this rock have been described 

 by M^^. Duchassaing and Michelotti, but so far as we can learn no 

 complete account of the rock or its fossils has ever been published. 

 It is worthy of notice that the elevation of its highest ridges above 

 the sea (less than 1300 feet) tallies very closely with that of 

 Barbados (1100 feet). 



(b) Ai)ti(/aa. — This island, which lies to the north of Guadalupe, 

 exhibits a very similar structure. Our knowledge of its geology has 

 not been enlarged since the publication of Dr. Nugent's Memoir in 

 1821 f. The island contains 108 square miles, and its westein 

 part consists mainly of volcanic rocks; but the whole of the north- 

 east portion, which is about half the superficial area of the island, 

 consists of coral-rock, the " marl " or " calcareous formation " of 

 Dr. Nugent. He describes its general aspect as a broken undulating 

 district, rising into round-backed hills and knolls, the highest of 

 which are between 300 and 400 feet above the sea. 



Of the rock itself he says : — " Throughout the greater part of 

 its extent this calcareous formation consists of a closely impacted 

 marl, readily broken down by the hoe or other means, and then 

 assuming a friable and pulverulent appearance, either of a white or 

 light yellowish colour, containing no other foreign admixture than 

 that of certain shells and corallines, and perhaps decayed vegetable 

 substances. Through this marl run in a great many places layers and 

 irregular masses, of various sizes, of a tolerably compact limestone, 

 which generally breaks into rounded fragments, containing a con- 

 siderable variety of fossil shells, nodules of calcareous spar, and small 

 patches and druses of cellular and crystallized quartz, chalcedony, 

 and agate." In other places there are included layers of siliceous grit- 

 stone, of smooth-grained calcareous sandstone (used for a building- 

 stone), and occasionally of puddingstone or breccia, with fragments 

 derived from the older rocks of the island. " The calcareous forma- 

 tion is replete with a variety of fossil shells and corallines, both in 

 a calcareous and a siliceous state ; but whether they are of different 

 species from those noAV inhabiting the surrounding sea future 

 observation must point out." 



In some portions of the rock the fossils are preserved in agate 



* Bates in Stanford's ' Compendium of Geography,' 2nd ed. p. 179. 

 t Trans. Geol. See. 1st ser. vol. v. p. 459, with map and sections. 



