58 Proceedings of Philosophical Societies. [Jult, 



being Compounded, as it would appear, of compact feldspar 

 eoloured black by an intimate solution of hornblende, and pos- 

 sessing as great a degree of fusibility as basalt itself ; it seems 

 referable to the trap family, and to be more nearly allied to 

 compact greenstone than to any other rock : it closely resem- 

 bles the substances that form the walls of the vein or dyke on 

 the coast, a little to the west of Seaport; intersecting there 

 alternate beds of basalt and amygdaloid. The trap which exhi- 

 bits vestiges of organized bodies in the north of Ireland is 

 evidently a formation of a much later era than that which cc«i- 

 tains analogous remains in the transition series, or in the first 

 floetz limestone. 



But these formations agree in this respect, that the organic 

 remains found in them correspond with those contained in the 

 • transition beds, the first floetz limestone or the chalk with which 

 they are connected ; and the inference, therefore, appears le^- 

 timate, that trap contained in those transitions and floetz rocks is 

 to be referred to a similar origin. 



May 5. — " A Notice on the Geological Structure of a Part of 

 the Island of Madagascar, and on some Specimens from the 

 Interior of New South Wales," by Prof. Buckland, was read. 



From the specimens from Madagascar which were chiefly 

 collected at Port Lougair, at the north-east angle of the island, 

 it would appear that a portion of the island consists of primitive 

 rocks, sandstone, and trap, and presents a similar geological 

 structure to the adjacent continent of Africa. The varieties of 

 granite which are found in the bed of the river Vaulaceen, that 

 runs to the above-mentioned port, are very similar to those 

 which commonly occur in Europe, e. g. fine grained grey 

 granite, large grained granite, containing flesh-coloured crystals 

 of felspar. The secondary rocks are varieties of sandstone, des- 

 titute of organic remains, and composed of grains of glassy 

 quartz intermixed with decayed felspar, but possessing no 

 strongly marked character by which they can be identified with 

 any of the known European series of rocks. A bright red sand- 

 stone, which is said to form the substratum of a hill called St. 

 George's, in the same district, is more decidedly characterized, 

 and seems to belong to the same class as enormous tracts of a 

 similar formation which occurs in the neighbourhood of the 

 Cape of Good Hope. It resembles in every particular of its 

 colour and composition the newer red sandstone of the English 

 series. 



Among the other Madagascar rocks are a clay porphyry 

 resembling that of Newton Glens in the couvity of Antrim, a fine 

 grained greenstone similar to some of those fovmd at the Giant's 

 Causeway, and a firmly compacted cream-coloured Hmestone 

 composed of granulated fragments of shells agglutinated by a 

 calcareous cement. 



The specimens from New South Wales afibrd indications 



