354 HALL’S EXCURSIONS. 
richly veined and beautifully transparent. It is traversed by 
a minute vein of perlstetn, towards the base. From the 
appearance of the cliff, we may suppose it to form a con- 
siderable stratum above the trachytes. M. Boussingault 
thought it probable the cliff had been partially hollowed 
out by the Indians, who anciently resorted to it, to procure 
materials for their arms and utensils. Obsidian is, I believe, 
generally considered a pure volcanic product, and Humboldt 
imagined the fragments scattered through the country to have 
been thrown out by the eruptions of Cotopaxi; yet in the 
neighbourhood of this volcano we found no traces of it, while 
here is an immense formation in situ, constituting apparently 
an integral part of the Cordillera. We remained only long 
enough for M. Boussingault to collect specimens, for the 
situation was by no means attractive. The thermometer stood 
at 38°, 11 a.m. We had not brought the barometer, but 
the vegetation and ascent indicated an elevation of betwixt 
14,000 and 15,000 feet. 
The next day on our return, we passed the farm of 
Oyamburu, memorable for being the southern extremity of 
the base measured by the Academicians on the adjacent plain. 
In the court-yard of the ruinous farm-house we found the 
stone on which they inscribed the compendium of their 
operations, published in their works. They had also erected 
a pyramid at each extremity of the base, but the barbarism 
of the inhabitants had long destroyed these monuments of 
science :—the stones were scattered, and the level plain 
extending from Oyamburu to the ravines of the Guaillapamba 
alone indicates by its uniformity the site of their measure- 
ments. We passed from Oyamburu to the village of Puembo, 
placed on the edge of the ravine of Guambi, and crossing 
that of Chichi by a Socabon bridge, arrived at Tumbaco, 
and returned the same afternoon to Quito. 
(To be continued. ) 
