164 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



the Atrato and a branch of the Andes which he supposed to exist west 

 of that stream in Colombia, a conclusion contrary to facts. The two 

 instances above mentioned are lineally arranged summits. Instead of 

 constituting a continuous trend, it will be seen that they are really 

 parallel ranges. 



With the above exceptions, long continued ridges, table lands, or 

 partially dissected plateaus are conspicuously absent, the whole topog- 

 raphy consisting of pointed hills from 200 to 1,500 feet in height, sep- 

 arated, sometimes encircled, by drainage valleys deeply incised and 

 cut down approximately to sea level. Our knowledge of the higher 

 summits and topography beyond the low drainage valleys is very defi- 

 cient. Exploring parties bent on establishing interoceanic connection 

 have followed the stream valleys from either coast, and explored only 

 the lowest passes separating their headwaters. 



While the surface in general is hilly, there are a few exceptional and 

 widely separated small areas of approximately level treeless upland 

 country. On the Pacific side, commencing at the mouth of the Bayano 

 and extending to the Cosla Eican boundary, occasionally open savannas 

 or treeless plains appear at an altitude far above that of the swamps 

 and present coast line. Some of these attain great extent, such as the 

 Plains of David in the ancient province of Chiriqui. 



In common with the whole Central American region south of Yuca- 

 tan, the Isthmus of Panama presents no such features as a well defined 

 coastal plain, like that bordering the eastern and southern margin of 

 the United States, and composed of the gently lifted and little deformed 

 marginal marine sediments. Such occasional levels as may be recog- 

 nized on either coast are the products of the erosion of the greatly 

 distorted sedimentaries and volcanic rocks. There are occasional 

 stretches of beach exposed at low tide, like that at Panama, but their 

 continuity is interrupted by abrupt cliifs and mountains coming pre- 

 cipitously to the sea. 



The Caribbean coast is generally marked by jagged and abrupt 

 bluffs, where the sea beats directly against the hills. The indentations 

 are slight and far apart. The same may be said of the Pacific side. 

 It is predominated by the great indentations of the Gulf of Panama, 

 dotted by numerous islands, having the same topography and general 

 aspect as the mainland. The shore line of this Gulf is itself indented 

 by many conspicuous inlets, far exceeding in size those of the Caribbean 

 shore, notably the Gulf of San Miguel, which is properly the mouth 

 of the Tuyra. (See Figure 1.) 



