216 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the low base level swamps which indent the valleys of the Rio Grande 

 aud 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 Mala and Mariato Point. Here 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 neai'ly all the details of the coast topography can be 

 seen. The interior consists of an east and west line of high coniaal 

 summits rising to a height of at least 2,000 feet, between which and 

 the coast were successively lower hills. The 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. It shows the wave-cut bluffs 

 rising from the water's level, and the higher peneplain Burmouuting the 

 bluffs and backing against the higher mountainous interior. The islets 



