294 NATURAL SCIENCE. April. 



denuded from large areas), about half of the continent, and the same 

 may be said of South America, though in both continents large areas 

 remain to be geologically mapped. It must be understood that I am 

 merely speaking in the rough, to convey the idea I wish to impress 

 upon those who read this, and subject to future correction. 



Though there are fresh-water and fluviatile deposits among these 

 rock-groups, especially in the Tertiary, the greater bulk are of marine 

 or estuarine origin. There are also great tabular masses of igneous 

 rocks5 especially in North America, and volcanic action has over all 

 the areas named played a prominent part from the Tertiary until 

 recent times. 



Although there is such a development of Cretaceous and 

 Tertiary rocks on the land areas, there is no doubt a great deal, we 

 cannot say how much, below the sea. The West Indian Islands give 

 evidences in their fauna of a former land-connection with South 

 America,^ and it may be that the whole area of the Gulf of Mexico 

 and the Carribean Sea is occupied by the same deposits overlaid by 

 great thicknesses of post-Tertiary accumulations. There is little 

 doubt that much of the sea-bed of the Behring Sea and the Aleutian 

 Islands, together with a strip of the sea-bed (none can say how 

 wide) along the western coast of North America, was land in 

 Pleistocene times, as proved by the discovery of mammoth remains on 

 Pribilof Islands and the N.W. coast of America,7 as also on Santa 

 Rosa, one of the largest of the coast islands of California*^; and it 

 is not improbable that Cretaceous and Tertiary rocks may occupy 

 much of this area also. 



Without traversing the whole of the known globe and making 

 incursions into the China Seas, Malayan Archipelago, New Guinea, 

 New Caledonia, Australia, and New Zealand, it may be well to 

 mention that Tertiary rocks are found far to the north on the land 

 bordering the Arctic Seas. 



It is in these Tertiary areas that the greatest mountain chains of 

 the world are situated, and it is further conceded by most geologists 

 that they are the highest because they are the newest and have not 



^See " Report on the Geology of the High Plateaus of Utah," 1880, U.S. Geo- 

 graphical and Geological Survey of the Rocky Mountain Region, by Captain C. E. 

 Dutton ; also, " A Geological Reconnaissance in Southern Oregon," by Israel Russell. 

 4th Annual Rept. of the U.S. Geol. Survey. 



'^See letter No. 3 by Alex. Agassiz to C. P. Patterson, on the Dredging Opera- 

 tions of the U.S. Steamer "Blake" from 1878-9. Bull. Museum of Comparative 

 Zoology, Harvard College, p. 299. 



7 Dr. Geo. Dawson, Q.J.G.S., vol. 1., pp. 1-9, 1894. 



^ " The Flora of the Coast Islands of California in Relation to Recent Changes 

 of Physical Geology," J. Le Conte, Bulletin viii., California Academy of Sciences, 

 PP- 515-520. Extraordinary fluctuations of level are also recorded in the successive 

 sea cliffs up to 1,200 feet above sea level in the island of San Clemente off the coast 

 of Southern California in Pleistocene times. See " Post-Pliocene Diastrophism of 

 the Coast of Southern California," by A. C. Lawson, Bulletin of the Department 

 of Geology, University of California, 1893. 



