1863.] DTINCAN WEST INDIAN CORALS. 409 



rests upon a trap-formation about 1400 feet high ; it forms hills 

 which are precipitous towards the trap, but have a gradual slope in 

 the opposite direction. It is stratified, and the beds, which dip at a 

 very considerable angle, consist of clays, limestones, and freestones ; 

 they are yellow in the last case, and green from the presence of 

 chlorite in the second. The clays contain crystals of felspar ; and 

 masses of porphyry, lava, greenstone, and amygdaloid are found 

 throughout the strata generally. 



The organic remains consist of "Woods, Corals, and Shells, either 

 silicified and fragmentary or, in the case of some Corals, converted 

 into chert-like masses. Two formations rest unconformably on the 

 Inclined Strata, namely, a deep Marl, whose surface is undulating 

 like our chalk-downs, and which forms the superficial structure of 

 the greater part of the Island ; and a Chert subordinate to the lowest 

 part of the Marl. The Chert does not rest conformably on the oldest 

 formation, is limited in extent, and has evidently suffered from 

 various wearing causes during the deposition of the Marl. It con- 

 sists of hard, opaque, white limestone-rock, mixed with portions of 

 coloured stone, and, from its position and organic remains, appears to 

 be an old coral-reef fringing the Inclined Strata, The specimens of 

 Corals occurring in it are siliceous and chert-like in appearance, and 

 the Woods are like those found in the more ancient strata. It is 

 characterized by the presence of extraordinary quantities of " Ceri- 

 ihia" which are rarely found in the Marl or in the Inclined Strata*. 



The Marl (the third formation), although its surface has suffered 

 greatly from denudation, reaches, nevertheless, to the height of 

 nearly 400 feet above the level of the sea, and consists of various 

 more or less compact limestones, white and yellow marls, and free- 

 stone, and contains vast quantities of Corals in different conditions 

 of fossilization. No fossil Wood is found in it, and the little chert 

 with Cerithia, occasionally met with, has evidently been broken off 

 the chert-rock and become intermixed. Agates, flints in great va- 

 riety of form and colour, calcareous concretions, and silicified Shells 

 and their casts are very common, and three or four kinds of Helix 

 also. Moreover, there are traces of bitumen. The depth of the 

 Marl, below the sea-level, is not known; but recent coral-reefs 

 fringe the low cliffs and outliers. 



The specimens in the Collection of the Society are derived from 



1. The Inclined Strata, or Conglomerate; 2. The Chert; 3. The 

 lower, middle, and upper parts of the Marl. 



Both the Inclined Strata and the Chert contain extraordinary 

 quantities of silicified Wood ; and their Corals, which are also silici- 

 fied, are often more or less rolled, and are found as agate mixed 

 with crystalline quartz, or are turned into opal ; they present imper- 

 fect calicular surfaces, but often consist of siliceous casts. The com- 

 pound Corals are all of great beauty, and Dr. Nugent identified them 

 invariably by their small patterns and chert-like appearance. 



The Marl contains no Wood, and its Mollusca are not identical with 

 those of the Chert ; and many species of Zoaniharia also occur in it 

 * The so-called " Cerithia''' probably belong to the genus Melania. 



VOL. XIX. PART I. 2F 



