506 Scientific Intelligence. 



indented by swamp levels, which for a distance at least from 

 either sea are filled with formations containing Pleistocene sea 

 shells. These are cutout of a matrix of greatly deformed Oligo- 

 cene and Eocene rocks. Below and contemporaneous with the 

 Eocene rock is a great series of igneous rocks, the latest of which 

 is found intcrbedded with the Eocene Tertiary. These consist of 

 tuffs of augite-porphyrite, olivine-basalt, trachyte, dolerite, andc- 

 sitic lava and rhyolitic pumice. A summary of the geological 

 evidence shows that the Isthmian barrier was closed at the close 

 of the Oligocene and has since remained land. 



Part III treats of the Pacific coast from Panama westward to 

 Punta Arenas, Costa Rica, showing characteristic elements of the 

 coast, including the wave-cut bluffs and elevated base-level plains 

 which, found upon both the islands and the main land, show that 

 the former are remnants which have been severed from the latter. 



Part IV deals with a continental section across Costa Rica 

 from Punta Arenas through San Jose to Port Limon. This 

 describes the gcomorphology and geology of this interesting sec- 

 tion of 115 miles across the high volcanic plateau of Central 

 America, which here rises to an elevation of nearly 11,500 feet. 

 It is shown that several well-defined base-leveled marginal plains 

 occur on both the Pacific and Atlantic sides of the continent as in 

 Panama. Much information is given upon the great volcanic 

 piles which rise above the sedimentaries of the lower coastal 

 region, which represent vast accumulations of volcanic debris 

 since Tertiary time. Attention is called to the line of interior 

 basins in which the chief centers of population and agriculture 

 are segregated, at altitudes of from 4000 to 5000 feet. A fine 

 illustration is given of the crater of Turrialba volcano, the most 

 eastern of the four great volcanoes along this section. A section 

 is also given from the summit of this eminence to the Caribbean 

 border which lies only a short distance from its eastern shore, the 

 details of which give much new information concerning the char- 

 acter of the folded Tertiary sedimentaries and their interbedding 

 with old volcanic extrusive lava. 



At Gualava, altitude 1400 feet, there are disturbed sedimentaries 

 containing interesting fossils of the Vicksburg formation as deter- 

 mined by Dr. Dall, which constitute the most southern known 

 outcrop of rocks of that epoch. In this section the volcanic rocks 

 also contain the interesting species theralite, which was recently 

 noted by Prof. J. E. Wolff in this Journal. In the basin valley 

 of San Jose, about 5000 feet above the sea, ancient looking lime- 

 stones were iound which were largely composed of Foraminifera, 

 Rudistes, shells of Inocerami and mollusca which very much 

 resemble certain formations of the Great Antilles adjacent to the 

 close of the Cretaceous and beginning of the Eocene Tertiary. 

 The occurrence of true granite at Siquires is noted as well as the 

 fact that granitic debris is found in the oldest sedimentary rocks, 

 indicating the existence of a pre-Tertiary granitic plexus in this 

 region. The interesting base-leveled, submerged, veneered and 

 reelevated coastal plains of Port Limon are also described. 



