200 The Naturalist in Nicaragua 
the very backbone of the continent, nbbing America from 
Patagonia to the Canadas—the fundamental gneiss which is 
covered, in other parts of Central America that I had visited, 
by strata of much more recent origin. Going down the 
valley of the Depilto the massive beds of quartz and gneiss 
are soon succeeded by overlying, highly inclined, and con- 
torted schists, and as far as where the road from Ocotal to 
Totagalpa crosses the river, the exposures of bed rock were 
invariably these contorted schists, with many small veins of 
quartz running between the lamine of the rock. On the 
banks of the river, from about a mile below Depilto, un- 
stratified beds of gravel are exposed in numerous natural 
sections. These beds deepen as the river is descended, until 
at Ocotal they reach a thickness of between two and three 
hundred feet, and the undulating plain on which Ocotal is 
built is seen in sections near the river to be composed entirely 
ofthem. These unstratified deposits consist mostly of quartz 
sand with numerous angular and subangular blocks of quartz 
and talcose schist. Many of the boulders are very large, and 
in some parts great numbers have been accumulated in the 
bed of the river by the washing away of the smaller stones 
and sand. Some of these huge boulders were fifteen feet 
across, the largest of them lying in the bed of the river two 
miles below Depilto. Most of them were of the Depilto 
quartz rock and gneiss, and I saw many in the unstratified 
gravel near Ocotal fully eight miles from their parent rock. 
Near Ocotal this unstratified formation is nearly level, ex- 
cepting where worn into deep gulches by the existing streams. 
The river has cut through it to a depth of over two hundred 
feet, and there are high precipices of it on both sides, similar 
to those near streams in the North of England that cut 
through thick beds of boulder clay. 
The evidences of glacial action between Depilto and 
Ocotal were, with one exception, as clear as in any Welsh 
or Highland valley. There were the same rounded and 
smoothed rock surfaces, the same moraine-like accumula- 
tions of unstratified sand and gravel, the same transported 
boulders that could be traced to their parent rocks several 
miles distant. The single exception was, I am convinced, 
one of observation and not one of fact, viz., I saw no glacial 
scratches on the rocks; but geologists know how rare these 
