I?17/NS OF THE ANCIENT MOUNTAINS. 317 



regions of the earth, and that its summits may very 

 probably have exceeded in height any now existing 

 in the world. What we now behold are the ruins of 

 the ancient mountains, and the singular conical peaks 

 are, as Liais has explained, the remains of some 

 harder masses of metamorphic gneiss, of which the 

 strata were tilted at a high angle. As the same 

 writer has remarked, although the crystalline rocks 

 are for the most part easily disintegrated, some por- 

 tions are formed of much more resisting materials, 

 and these have to some extent survived the incessant 

 action of destructive forces. 



We are far from possessing the materials for a 

 rational estimate of the probable extent and elevation 

 of the ancient mountain ranges of Brazil. In the first 

 place, we have a plateau region occupying a large 

 part of the upper basin of the Parana, with an area of 

 fully 100,000 square miles, covered with detritus to 

 an unknown, but certainly considerable, depth. In 

 addition to this, it cannot be doubted that the finer 

 constituents carried down by that river, and its 

 tributary the Paraguay, from the same original home, 

 have largely contributed to the formation of the 

 Argentine pampas and Paraguay, including the 

 northern portion of the Gran Chaco. Borings and 

 chemical analysis of the soil may hereafter give us 

 reliable data ; but in the mean time we may safely 

 reckon that an area of 200,000 square miles has been 

 mainly formed from the materials derived from the 

 ancient mountains whose importance I endeavour to 

 point out. In addition to all this, we should further 

 reckon the soluble matter and fine silt carried to the 



