86 ME. E. B. NEWTON ON FOSSILS FEOM MADAGASCAR. [Feb. 1895, 



it has also been doubtfully referred to a Permo-Carboniferous 

 horizon by Cortese (op. cit. Boll. R. Com. geol. Ital.). One of 

 the specimens collected by Mr. Baron shows the cell-structure of 

 Ec[uisetum (fide W. Carruthers, E.R.S.), and another appears to be 

 an impression of a fern. 



IV. Note on the Stetjctuees of some Limestones 

 feom Madagascar. 



A number of limestones collected by Mr. Baron from various 

 localities, extending from Jangina, in South-west Central Mada- 

 gascar, to the northern parts of the island, have been carefully sliced 

 and microscopically examined. They mostly present ordinary 

 oolite structures, the granules exhibiting the usual concentric and 

 radiate characters. Many of these limestones contain organisms 

 such as foraminifera (Cristettaria, Textularia, Marginulina, etc.), 

 mollusca (Nerincm), polyzoa, corals, etc., but the most interesting 

 form determined is that of Girvanella, which appears to enter 

 largely into the composition of these rocks. The minute tubules of 

 this genus, which occur in spherules of a variety of sizes, are best 

 seen in a black crystalline rock obtained from W. of Ankaramy, 

 off the north-western coast. The Girvanella -spherule in this 

 specimen is extremely large, and measures 10 mm. in diameter. 

 Another limestone from the Antankarana province exhibits a 

 similar structure, and according to Mr. Wethered resembles his 

 species G. pisolitica, 1 from British Jurassic strata. This genus, 

 although regarded at the time of description by Messrs. Nicholson 

 and Etheridge, Jun., as possessing rhizopodal affinities, is now 

 generally considered to belong to the calcareous algae. It has a 

 wide distribution both geographically and geologically, having been 

 discovered in limestones ranging from Cambrian to Jurassic times, 

 and is recorded from Britain, Europe, America, and Australia. 

 None of the organisms mentioned, however, assist one to fix the 

 precise age of the rocks in which they are found, although I am in 

 favour of assigning them to the Jurassic period, and this chiefly on 

 account of the presence of a brachiopod allied to Hhynehonella 

 plicatella in one of the limestones collected from the neighbourhood 

 of the River Lokia or Loquez, and from which many of these rock- 

 specimens were procured. 



Lastly, a microscopic examination has been made of the Cretace- 

 ous limestone forming the Ambohimarina hill, in which the specimen 

 of Lampadaster was discovered. This having been proved to 

 be largely composed of Globigerince, it is suggested that it be 

 termed a Globigerina-limestone. 



1 Geol. Mag. 1889, p. 196, pi. vi. figs. 10, 11. 



