432 Geological Society : — 



most part at least, Archaean, llecent deposits fringe the coasts aud 

 are largely developed on the southern part of the island. 



East of the central line of watershed there is a long depression 

 containing a wide alluvial deposit, probably an old lake-bed. Ter- 

 races fringe its sides in many places. The lagoons of the eastern 

 coast are due to alluvial deposits. 



The paper concluded with some remarks on the geological antiquity 

 of the island, its separation dating from earlj^ Pliocene times, if not 

 earlier. This is the conclusion arrived at by Wallace from its fauna ; 

 the author's detailed researches into its flora, recently described 

 before the Linnean Society, show that while about five sixths of 

 its genera of plants are also found elsewhere, chiefly in tropical 

 countries, at least four fifths of its species are peculiar to Madagascar. 



The Appendix, drawn up by Mr. R. BuUeu Newton, P.G.S,, 

 consisted of Notes upon the fossils collected by the author, with 

 tables, aud descriptions of two new species, iiamely, Astarte (?) 

 Baroni and Splicera madagascariensh, both from deposits of Lower- 

 Oolitic age. 



3. " Notes on the Petrographical Characters of some Eocks col- 

 lected in Madagascar by the Rev. R. Baron." By F. H. Hatch, 

 Ph.D., P.G.S. 



This paper was divided into two parts, the first treating of the 

 petrographical characters of the older crystalline rocks of the eastern 

 and mountainous part of the island, the second of the nature of 

 the lavas that have been erupted from volcanic vents situated 

 mainly iu the same portion of the island. 



i. The Older Crystalline Rocks are represented in Mr. Baron's 

 collection partly by foliated specimens, partly by rocks showing no 

 parallel structure in the hand-specimen. 



The foliated specimens have, with few exceptions, the structure 

 and composition of gneiss. The author subdivided them into an 

 acid and a basic scries. The acid series, which embraces rocks com- 

 posed of abundant quartz with orthoclase as the dominant felspar, 

 he terms granitite-gneiss ; the basic series, which consists of rocks 

 containing little quartz and much plagioclase felspar, tonalite-gneiss. 

 The unfoliated specimens comprise granite, gahhro or norite, 

 pijroxene-gramdite, and pyroxenite. 



The majority of the granites are of the granitite-type — i. e. they 

 are granites with one mica ; but granites ivith tivo micas are also 

 represented. 



The remainder of the rocks are of a basic type. They are inte- 

 resting, in the first place, on account of the striking combinations of 

 fresh and beautiful minerals they present, as, for example : — plagio- 

 clase, hypersthene, olivine, brown hornblende and green spinel, in 

 an olivine-norite ; or, plagioclase, green pyroxene (omphacite or 

 diallage), hypersthene, hornblende, garnet and iron-ore, in pyroxene- 

 granulite; or, again, diallage and hypersthene in j:)?/roA'e;(i^e. 



But of greater interest is the fact that these basic types, which 



