HALL’S EXCURSIONS, 345 
the soil is a hard ferruginous clay, which needs artificial 
irrigation, and this is scanty, because both the river of 
Guaillapamba and its tributary streams bury themselves in 
deep ravines. Between Cambaya and Tumboco it is crossed 
by what is called a Socabon Bridge. This is one of those 
contrivances which seem entirely due to the Spanish settlers. 
The Incas employed bridges of twisted bushes to cross the 
larger rivers; and I am not aware that in Europe we have 
any model of a Socabon Bridge. Socabon means a cavity. 
To form the bridge, a tongue of land is selected on one side 
of the river, capable from its breadth of being readily per- 
forated: an arch, or vault, is then worked through it, without 
aid of masonry or timber: when it is completed, the channel 
of the river is deepened so as to give the current a direction 
through the aperture, and the old bed being thus abandoned, 
the perforated tongue of land forms a bridge over the new 
course of the stream. This may be more readily understood 
by the sketch, (Tas. CXLIV.) where A is the original bed 
of the river; B the perforated tongue of land; C the road. 
The traveller, who is not aware of the circumstance, is often 
puzzled to find how he has crossed the river, without having 
met with a bridge. One might, at first sight, imagine these 
bridges the work of Nature, but the old course of the stream 
plainly indicates that its change is artificial. We shall meet 
with another of these bridges in our present excursion, and 
there is a third near Guaranda, on the road from Guayaquil. 
The inhabitants of Aculato have been several years employed 
in forming one to cross the river near this town. These 
bridges have the advantage of needing no repairs, and of 
lasting, one cannot say how long. 
The village of Tacabuco is larger than Ambaya, but nearly 
of the same , description ; the distatiee betwixt them is almost 
aleague. Proceeding about two miles, we crossed the ravine 
of Chichi. This is one of those tremendous fissures which 
are frequent in all the district of Quito. It extends from 
the base of the eastern Cordillera to the course of the 
Guaillapamba. Its depth is about 1000 feet, more, rather 
Sgconp SERIES. 2x 
