164 BULLETIN: MUSEUM OF COMPARATIVE 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 Costa Rican 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 cliffs 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.) 
