106 M. Boussingault's Account of 



crystals of glassy felspar, is coloured by augite ; the crystals of 

 felspar are rather rare, and the mass has often the air of a ba- 

 salt ; but I have never seen olivine in it. Sometimes this rock 

 is compact and arranged in prisms ; sometimes filled with holes 

 hke scoria. One would then be inclined to regard it as lava, if 

 it covered considerable spaces ; but it occurs always in frag- 

 ments, which rarely have the size of a fist. This rock is evi- 

 dently of very recent origin. At Chorrera de Pisque, near 

 Ibarra, there is a beautiful colonnade, reposing on alluvium ; on 

 the estate of Lysco, this substance, in the condition of fragments, 

 has formed a passage for itself through the trachyte, which has 

 been elevated by its agency. It is there where Humboldt be- 

 lieved he saw a stream of lava {coulee), which had issued from 

 Antisana. In another memoir I have explained the reasons 

 which have induced me to differ from the opinion of my illus- 

 trious friend. The extinct volcano of Calpi, placed at the foot 

 of Chimborazo, also consists of this kind of basalt. We visited 

 it on our return from Rio-Bamba. 



In the midst of the sand which covers the whole plain of Rio- 

 Bamba, there is a hill of a dark colour, called the Jana-urcu 

 (the black mountain). 



At the lower part of this hill trachyte projects through the 

 sand ; it is of the same nature as that on which, at some dis- 

 tance, Chimborazo rests. This trachyte seems to have been 

 thoroughly shattered ; it is full of clefts and fissures in all direc- 

 tions. The acclivity of the Jana-urcu, towards Calpi, consists of 

 small fragments of the black rock, whose heaping together com- 

 pletely reminds one of the stone-eruption of Lysco. It appears, 

 indeed, that this eruption of the Jana-urcu, took place after the 

 deposition of the sand which covers the plain ; for in the vicinity 

 of the volcano the ground is covered with black scoriaceous 

 stones. 



Our guides, Indians from Calpi, conducted us to a cleft, 

 where the sound of a subteiTanean waterfall was distinctly heard ; 

 and, judging from the loudness of the noise, the mass of water 

 must be considerable. 



The unproductiveness of the soil, from Latacunga to Rio- 

 Bamba has often surprised me. 



I asked myself why the glaciers of the high mountains, which 



