GEOLOGICAL FORMATION. 31 



line of igneous disturbance from the extreme northern point 

 of Madagascar to at least as far south as the twenty-third 

 parallel ; and from the appearance of a line of hills seen at a 

 distance south of this latitude, I am strongly inclined to 

 believe that there has been subterranean agency at work even 

 beyond the upper granitic plateaux, but no examination has yet 

 been made of this southernmost region. 



With regard to the geology of Madagascar, but little is at 

 present known with any exactness, for no competent geolo- 

 gist has yet made a systematic examination of the country. 

 There are, however, a few facts of a general character which 

 have been noted by various observers, and these may be here 

 collected together as a slight contribution to a knowledge of 

 this subject, pending a more complete and scientific treatment 

 of it. 



As already mentioned, the elevated region which forms so 

 large a part of the central, northern, and eastern portions of 

 the island is largely composed of Primary and igneous rocks. 

 Granite, gneiss, and basalt are present almost all through 

 this high region, and generally form the loftiest points in the 

 country. In a single hill there is often a considerable variety 

 of rock both in colour and texture — granite of various shades 

 of grey, red, and rose-colour, with the constituent parts both 

 fine and coarse. Veins of quartz, running both through these 

 and the clays by which they are overlaid, are often met with, 

 and very fine specimens of rock-crystal are frequently found. 

 A hard, whitish, and durable stone, which has some resem- 

 blance to the Yorkshire stone called Bramley Fall, is used 

 in Antananarivo for public buildings, as well as for the 

 native tombs. 



The lower hills, as well as the high moors, are usually com- 

 posed of a bright red clay, but below the surface this often 

 seems to pass into a light pink or white earth, resembling 

 kaolin or china clay. This frequent change of colour would 

 lead one to infer that atmospheric influences had something 

 to do with the difference between the surface clay and that 

 exposed in the numerous precipitous clefts which the rains 

 excavate on the hillsides. In many places the material 

 found amongst the rock seems exactly like granite in its con- 



