Geology and Mineralogy. 507 



A comparison of the Panama and Costa Rica sections is then 

 given, together with an interesting tabular summary, page 236, 

 of the known formations and events. 



In working out the great amount of original data conoerning 

 the detailed geology of these hitherto little known regions, the 

 author was assisted by the minute studies of several specialists 

 whose reports are of greatest value, among which may be men- 

 tioned the reports of Dr. W. H. Dall on the Tertiary mollusca ; 

 Prof. R. M. Bagg on the Foraminifera ; Prof. J. E. Wolff on the 

 igneous rocks; Mr. H. W. Turner, who made valuable microscopic 

 studies of certain peculiar and difficult earths of volcanic origin ; 

 Mr. Ahe Sjogren, and Mr. T. Wayland Vaughan. The special 

 reports by these authorities are published as appendices to the 

 work and are each valuable contributions which should be sepa- 

 rately noticed. 



Having secured in personal study and observation a foundation 

 for making deductions, the author in Part V discusses the 

 11 Union of the Continents and the Problems of the Straits," set- 

 ting forth a resume of the geology of the Central American main- 

 land, showing the present condition of knowledge thereof so far as 

 the incompleteness of exploration will permit. A concise resume 

 is made of the entire geologic sequence. Interesting facts are 

 presented indicating the existence of a granitic basement, which 

 show that there is room in this belt alone for much study. Atten- 

 tion is called to the burial of the Paleozoic rocks between the 

 southern boundary of the United States and the equatorial South 

 America by the vast accumulations of the Mesozoic sedimentaries 

 in Mexico and by volcanic and Tertiary material in Central 

 America, the only outcrops of fossililerous Paleozoic rocks known 

 between these regions being the Carboniferous strata of Guate- 

 mala and Chiapas as desciibed by Dv. Sapper. 



The Pre-Cretaceous Mesozoic seems to be as problematical in 

 these tropical regions as it is in the United States. The writer, 

 however, calls attention to localities in Mexico and Guatemala 

 which have striking stratigraphic analogy to the Red Beds of the 

 western interior region of our own country. 



A chapter on diastrophism and vulcanism deals with interest- 

 ing facts of orogenic history, the most important of which is oro- 

 genic revolution of late Tertiary time, which, according to Mr. 

 Hill, seems to have been the dominating factor in producing the 

 present conspicuous features of Central American and Antillean 

 geography, and to have been instrumental in producing the great 

 east and west corrugations aud troughs of the American Mediter- 

 ranean which have been described by others as the river valleys 

 of submerged continents. 



The evidence of former periods of marine connection in the 

 Isthmian region is dealt with in extenso. The conclusion is 

 reached that there is some evidence that a land barrier severed 

 the two oceans as far back in geologic history as Jurassic time 

 and that this barrier may have continued through the Cretaceous 



