Yol. 68.1 GEOLOGY OF COSTA KICA. 139 



continents of North and South America. His observations on 

 the extension of land, not only westwards but also eastwards in 

 the direction of the Antillean Continent, raised the question of the 

 permanence of continental and oceanic areas, and it was very 

 interesting in this connexion to learn that the strike of some of the 

 rocks described was across the isthmus and transverse to the general 

 trend of the great mountain-ranges. 



Dr. J. W. Eyans said the evidence that the Author had brought 

 forward, showing a connexion between the Gulf of Mexico and the 

 Pacific by way of Costa Rica, was of considerable interest, for it 

 was recognized that South America was separated from the northern 

 continent after early Tertiary times. Late in the Miocene, South- 

 American types appeared in N'orth America, but it was not until 

 nearly the close of the Pliocene that transmigration in the opposite 

 direction took place. This had been explained by supposing that 

 a portion of Central America was connected with South America 

 while separated from the land to the northward, and that subse- 

 quently it was detached from the former and united to the latter ; 

 but that a considerable time elapsed before the bridge between the 

 two continents was complete. He suggested that the marine tract 

 described by the Author constituted the northern boundary of that 

 portion of Central America which was connected alternately with 

 the two continents. 



He was much interested in the torrential deposits mentioned by 

 the Author. He had himself published a short paper in the 



* Geological Magazine ' on similar deposits north-east of the 

 Eolivian Andes. Phenomena of this nature had been recently 

 described by Dr. Hauthal from the borders of the Argentine and 

 Bolivia, where the torrents of water and rock-fragments that from 

 time to time poured out from the mountain-gorges were termed 



* volcanoes ' by the inhabitants. 



The Author, in reply, stated that he fully appreciated the kind 

 way in which the Pellows had received his paper. With regard to 

 the intercontinental land-connexion discussed by Dr. Evans, he 

 pointed out that certain evidence existed of a former land-mass to 

 the west of Central America, which might have accounted for some 

 of the phenomena of migration. 



a. J. G. S. No. 270. 



