590 POPULAR SCIENCE MONTHLY. 



Central America, and Dr. Maack and others have suggested a con- 

 nection at some previous time. By Mr. F. C. jiSTicholas enougii 

 data have been gathered to make it appear tliat 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 hun- 

 dred 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 di\'ide 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 N'icaragua, 

 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 



