68 BEV. E. BAEON GEOLOGICAL NOTES [Feb. 1895, 



which, nevertheless, they are always subsidiary. The limestones in 

 this locality are very largely composed of lamellibranchiata, such 

 as Astarte Baroni, etc. 1 These lie about on the ground (having 

 weathered out from the matrix) in such quantities that they might 

 be literally gathered in cartloads. This frequent alternation of 

 sandstone and limestone would seem to point to a successive 

 rising and falling of the land in this part of the island at the time 

 of their deposition . 



Some 4 or 5 miles north of Andranosamonta (300 or 400 feet 

 above the sea and a mile or two from the shore) the limestone, as 

 shown by its fossil contents, belongs to the Oxfordian series, one of 

 the commonest species being PerispJiinctes {Ammonites) polygyratus, 

 Reinecke. This lies on the surface of the ground in great numbers, 

 but unfortunately the limestone in which it is embedded has decayed 

 into a mere clay, and thus the fossils are in a bad state of preservation,, 

 both they and their matrix being abundantly occupied by septaria 

 filled with calcite. A few miles west of Ankaramy occurs a black 

 crystalline limestone, which, according to Mr. R. B. Newton, con- 

 tains an organism called Girvanella. At Andranosamonta itself I 

 was fortunate enough to find parts of the first fossil reptile that has- 

 been discovered in the island. It proves to be a new species of 

 Steneosaurus, which Mr. R. B. Newton has named S. Baroni. 2 It 

 may be noted that immediately north of this village selenite occurs 

 in the clay. 



This belt of low-lying land on the north-western coast consists 

 therefore mostly of sandstone, though limestone is also abundant, 

 the predominant dip of both being very slightly seawards. The 

 sandstone is mostly of medium grain and brownish colour, and 

 generally turns red in weathering. In some places spherical or oval 

 nodules, about the size of a hen's egg, of ferruginous matter which 

 has probably segregated from the surrounding mass, jut out from 

 the exposed surface of the rock. Fossils gathered from the lime- 

 stone show it to be mostly Jurassic, but occasionally Cretaceous 

 (Neocomian), and on the coast-line mainly Focene (Nummulitic- 

 Limestone). That this portion of the island has been recently 

 elevated above the sea to the extent of at least 200 or 300 feet 

 has been already stated ; to this I need not therefore again recur. 



In Quart. Journ. Geol. Soc. vol. xlv. (1889), pp. 326, 327, I 

 spoke of some strange rocks resembling erratic blocks lying on the 

 surface of the ground in the neighbourhood of the village of 

 Mahitsihazo (long. 48° 5' E., lat. 14° 17' S.), whose existence I 

 could not then account for, suggesting, with a good deal of doubt, 

 that they had been possibly brought there by glacial action. The 

 difficulty of accounting for their occurrence is now solved. I find 

 from microscopical examination that these rocks are trachyte. But 

 how came the blocks into their present position ? The explanation 

 is simple. Nearly the whole of this low-lying land, from the village 



1 See Mr. E. B. Newton's paper (p. 78) for names of other fossils found 

 here. 



2 Geol. Mag. 1893, pp. 193-196, pi. ix. 



