216 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the low base level swamps which indent the valleys of the Rio Grande 
and border the coast of Panama, the residual clays present the same 
laminated structure. The laminated red clays can be continuously 
traced from Culebra as far north as Gorgona, everywhere overlying 
the massive igneous rocks and some of the igneous boulder formations, 
and I am inclined to think that some of them, with the exception of 
the swamp levels, are the residuum of the Tertiary sediments. 
PART III. 
The Pacific Coast from Panama to Punta Arenas, Costa Rica. 
Leaving the island of Naos in the Bay of Panama at night, we 
reached Cape Mala, the outer point of the Gulf, the next morning. 
After turning the point of the cape, we sail close alongside the straight 
shore line between Cape Male and Mariato Point. Неге the Pacific 
breaks abruptly against what is perhaps the widest portion of the 
Isthmian mainland. The accompanying sketches (Figs. 17-21) will 
convey an idea of the general topography of this region. From the 
steamer’s deck nearly all the details of the coast topography can be 
seen. Тһе interior consists of an east and west line of high conieal 
summits rising to a height of at least 2,000 feet, between which and 
the coast were successively lower hills. Тһе higher summits are more 
elevated in general than along the line of the Panama Railway section, 
but they present the same type of configuration. 
At the water's edge the coast shows in many places low vertical 
bluffs from 20 to 100 feet, which are being attacked by the washing of 
the waves. Sailing parallel to these bluffs and within a half mile of 
them we could make out the same familiar red clay so universal in the 
Isthmian region. Sometimes there were beds which were apparently 
stratified and not of igneous origin. Again the massive igneous rocks 
would predominate; they are especially conspicuous as we approach the 
western end of this headland. At one point we could see black stratified 
rocks, resembling shaley clay or green sandy marl, with strong dips to 
the northward. 
The accompanying sketch of Mariato Point (Fig. 17) gives most of 
the characteristic elements of this coast. Tt shows the wave-cut bluffs 
rising from the water's level, and the higher peneplain surmounting the 
bluffs and backing against the higher mountainous interior. The islets 
