32 LIME AND SLATE. 



stituent parts, but without the cementing element, so that it 

 can be cut quite easily by a spade. The red clay is some- 

 times varied by a light brown clay on the hills, while the 

 plains and valleys are filled with rich alluvial clays, blue and 

 black in colour. In all these clays there is an apparently 

 total absence of all organic remains, either animal or vege- 

 table, so that it is not an easy task to determine their geolo- 

 gical age ; and there is little sign of stratification, although 

 I have detected some appearance of this in the rocks, with 

 tilting of the strata. 



In this elevated region there seem to be few, if any, 

 sedimentary rocks of a more recent age than the Primary 

 ones which are so prominent a feature of it. A soft dark- 

 red stone is found in some places, but this appears to be only 

 a hardened clay. Columnar basalt has been noticed at some 

 points, as well as extensive beds of volcanic ash, decomposed 

 lava, scoria, and lava rock of all varieties of hardness, in 

 some of which, crystals of olivine are found in abundance. 



At one point, however, in the upper region of the island, a 

 limestone deposit occurs. This is at Sirabe, to the south-west 

 of the Ankaratra mountains ; and from the pits dug here 

 most of the lime used for building in the central province is 

 procured. It has not yet been examined by any one with 

 competent scientific knowledge, but it appears to be a 

 sulphate of lime, and is probably only a local deposit and 

 not a stratified rock, and most likely is connected with the 

 subterranean action so visible all around the district. Jets 

 of carbonic acid gas are found in the plain among the lime, 

 and from one of the springs which rise up to the surface a 

 rock has been deposited with stalactite caves in its sides. 



Clay-slate is met with in the southern part of this elevated 

 region, and in the Bdtsileb country a valuable slate, suitable 

 both for building and for writing upon, is found, although it 

 has not yet been worked to any extent. The royal chapel at 

 Antananarivo is roofed with this native slate. According to 

 some accounts, greywacke or whinstone, silex, and chert, with 

 chalcedony, are also met with in the southern highlands. 



Prom certain of the facts above given, as well as from 

 other considerations, it appears highly probable that this 



