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Outcrops of a gneissoid schist on the valley sides and rapids in the stream bear witness to the youthfulness of this portion of the river channel.

These slaty and gneissoid planes are seen to be parallel to the direction and attitude of the sediments, wherever they are near enough for comparison.

It produced effects varying from granite with a rude gneissoid appearance, through a banded fine gneiss, into a fine quartz schist or slate.

At this distance, rapids commence, and the bed of the river exhibited greenstone and gneissoid boulders.

We started on our return down the valley at three o'clock, and took particular note of the succession of the rocks, as I had become much interested in finding these quartz and gneissoid beds, which I had no doubt were the same Laurentian rocks that I had seen in Canada and Brazil—the very backbone of the continent, ribbing 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.