Geology and Mineralogy. 505 



tra; volume III gives memoirs on Rontgen Rays, etc. The con- 

 tinuation of the Series is stated to depend upon the success of 

 these opening volumes. Of their great value to all students and 

 workers in physics there can be no possible question, and it is 

 heartily to be desired that the response of the public may be 

 sufficiently prompt and generous to justify the publishers in going 

 on with the work. 



II. Geology and Mineralogy. 



1. The Geological HUtory of the Isthmus of Panama and 

 Portions of Costa Mica. Based upon a reconnaissance made for 

 Alexander Agassiz ; by Robert T. Hill, with special determi- 

 nations by William H. Dall, R. M. Bagg, T. W. Vaugban, J. E. 

 Wolff, H. W. Turner, and Ahe Sjogren, with nineteen plates. 

 Bulletin of the Museum of Comparative Zoology at Harvard Col- 

 lege, vol. xxviii, No. 5 (Geological Series, vol. iii), Cambridge, 

 Mass., June, 1898.- — This work of 285 pages, with nineteen plates 

 and twenty-four figures, only claims to be a reconnaissance, yet it 

 is a very thorough summary of the known geomorphology, 

 geology and paleontology of the Isthmian and Central American 

 regions, dealing with those problems which pertain to the union 

 of the continents and the existence of pre-historic Isthmian 

 straits. It is based upon two transcontinental sections, one of 

 which was made across the Isthmus of Panama and the other 

 across the Republic of Costa Rica, to which is also added the 

 results of the late W. M. Gabb's explorations in Talamanca, about 

 midway between the two sections explored by Mr. Hill. 



Part I of the work deals with the geographic position of the 

 Isthmian region, showing the independent position of the North, 

 Central and South American orogenic systems ; the physical dif- 

 ferences between the lands surrounding the Caribbean and the 

 Gulf of Mexico, the distinction of the present volcanic regions 

 from those of volcanic quiescence and the relation of the volcanic 

 mountains to the areas composed of folded sedimentaries. 



The geomorphology of the Isthmus of Panama is dealt with at 

 length, showing that this barrier between the oceans is an old 

 degraded land cut up into numerous summits and void of a well- 

 defined axial backbone. Its topography is contrasted with that 

 of the higher Andean region to the south and the Costa Rican 

 plateau to the north. A summary of the topographic evidence 

 shows the relative antiquity of the Isthmian land and that it is a 

 remnant of a much wider area, the former seaward extensions of 

 which in the now submerged marginal platforms are well shown 

 upon profiles and maps. 



Part II treats of the geology of the continental section across 

 the Isthmus of Panama, giving in minute detail every feature of 

 the brief 40 miles which there separate the two oceans. All the 

 rocks are described, beginning with the low recently elevated 

 coral reefs on the Atlantic side. The coast of both sides is 



