59 
which we were ied at first to mistake for those 
bats of gigantic size so well known in the equi- 
noctial regions. Thousands of them are seen 
flying over the surface of the water. The In- 
dians assured us^ that these birds are of the size 
of a fowl^ with a curved beak and an owl’s eye. 
They are called cacas ; and the uniform colour 
of their plumage, which is a brownish gray, leads 
me to think, that they belong to the genus of the 
caprimulgus, the species of which are so various 
in the Cordilleras. It is impossible to catch 
them, on account of the depth of the valley ; and 
they can be examined only by throwing down 
rockets to illumine the sides of the crevice. 
The height of the natural bridge of Icononzo 
above the ocean is eight hundred and ninety- 
three metres. A phenomenon, similar to the 
upper bridge, of which we have just given the 
description, exists in the mountains of Virginia, 
in the county of Rockbridge. This Mr. Jeffer- 
son has examined with an attention, that distin- 
guishes all the observations of that excellent 
naturalist The natural bridge of Cedar 
Creek in Virginia is a calcareous arch of twenty- 
seven metres at its opening ; its height above 
the waters of the river is seventy metres. 
The earthen bridge (Rumichaca), which we 
found on the declivity of the porphyritic moun- 
* Notes on Virginia^ p. 66, 
