Central America, and Dr. Maack and others have suggested a connection at some previous time. By Mr. F. C. Nicholas enough data have been gathered to make it appear that a geological strait and later a canal or canals obtained similar to that of Tehuantepec. The barrier between the low navigable waters on each side of the divide is only eleven miles across, and of this distance, the valley is so low that except for three miles of its course it is navigable for canoes at all times. During floods even the remaining three miles can be crossed in small boats. This passage is only about a hundred and fifty feet above the sea, but it is a narrow canal a hundred
Fig. 9.—The Divide of the Isthmus of Tehuantepec (view on larger scale than in Fig. 8), showing the northern end of the geological canal dissecting the divide to a depth of about one hundred and fifty feet. Knob to the left represents the end of a ridge rising out of the old geological strait.
feet or more below the summit of the dividing ridge. The barrier in part appears to have been produced by the delta deposits brought down from the lateral mountains by the streams at a time when the valley was occupied by the waters of a great strait from twenty to forty miles wide, connecting the Caribbean Sea with the Pacific Ocean. Some of these gravels contain large quantities of gold. The gold-bearing gravels and other alluvial deposits which rise upon the hillsides and occur on the divide seem to mark the different changes of level corresponding to those in the Tehuantepec Isthmus.
Besides this Atrato Strait, connecting the Caribbean Sea with the Pacific Ocean, there was another connection by way of Nicaragua, as suggested by Mr. Crawford's studies, but the latest geological canals across this region have been obstructed by barriers rising to two hundred and thirty feet. The more open country of the Panama
