374 Geographical Notices. 
porphyritic in texture, and schistose in structure. Layers of an 
argillaceous sedimentary rock of little specific gravity, stratified 
but bearing marks of disturbance, since their original deposition 
are overlying the former. In the bed of the river, erratic and 
drifted boulders of concretionary or semi-rock occur. Alluvium 
uniformly covers the whole. e lower strata are only ex 
at the east end of the section and partly along the Truandé. 
From the mouth of the Nercua upwards only quaternary depos 
its are standing out. | 
The upheavings of the metamorphic rocks rise toa height 
(approximately of from 250 to 800 feet) above the waters of the 
ruandé; and form here a series of falls and rapids, the river 
rushing through the narrow pass of this formation for the dis 
tance of about three miles. : 
This catenary mountain range, made up of this rock, seems to 
be a northeasterly outrunner of the Cordillera to the west, and 
has received from the surveying party the name “Sierra de los 
Saltos ;” for under the vernacular name “ Saltos” this region 1s 
known to the natives. 
Not only within the enclosures of the mountain pass of the 
Saltos, but all through the table-lands and their next vicinity 
below, more distinct potamographical features are perceptible 
They consist of a number of real tributaries, each one draining 
a regular basin of its own. This is quite different from the 
swampy sections below, the whole extent of which is to wee 
sidered as a common estuary, where all the _affluents of so 
Atrato and Truando lose their identity beneath the dead 
of a network of lagoons and sloughs. oS ae 
On the western limits of the table-land interesting s1g% 3 
a volcanic axis were observed in some thermal springs, 0° 
which was found to have a temperature of 107° F. 
water is saline and smells like carburetted hydrogen. iad 
On the surface of the table-lands the array of Vv This 
animal forms, reaches its highest pitch of dovelapote ad 
insolation of the country, in addition to a bens pein 
and a diversified sloping of the surface. vee taken 284 
permanent abode, to follow, though constantly roaming, 
+i of 
Here also the plague of mosquitos and sandgnats cen 
ally; but now the traveller has to guard against the 
perceptible aggressions of the “nigua” (Pulex Poa especially 
Articulata in general appear still more diversified, maber of 
idee, Formicide and Cimicide, as also a great pa rai 
vood-destroying Coleoptera. Xylocolous and troglonydopter® 
nidz, become quite a prominent feature, while shes | 
