320 



SCIENCE. 



[N. S. Vol. VIII. No. 193^ 



The elevation of the West Indies took 

 place at this date, and these islands were 

 peopled from the South American coast. 

 What we already know of the rapid evolu- 

 tion of molluscs, insects and mammals on 

 these islands shows how closely dependent 

 variation and adaptation are on isolation as 

 well as changed topographic and climatic 

 features. 



These problems have been studied with 

 great care in the Hawaiian Islands by Gu- 

 lick, and more recently by Hyatt. As well 

 stated by Wood worth : " With the develop- 

 ment of the umbrella-shaped topography of 

 the Island of Oahu the land shells have 

 varied from common ancestral coastal type 

 to valley-cradled, differentiated varieties 

 in the upper and disjointed valleys of this 

 dismantled, volcanic island cone."* 



The limits of this address do not permit 

 ns to treat at length of the wonderful 

 changes, both geological and zoological, 

 which occurred in western America during 

 the Tertiary. They are now familiar to 

 every one. The geological changes were 

 very great and widespread, as shown by the 

 elevation of the land at the close of the 

 Miocene. Fragments of the Cretaceous sea- 

 bottom, with horizontal strata, occur in the 

 Eocky Mountains at a point about 10,000 

 feet above the sea. The inland Cretaceous 

 sea was drained off and replaced by a series 

 of fresh-water lakes, beginning with the 

 Puerco, or the lowest Eocene, and ending 

 with the Pliocene lakes. 



The most salient biological features of 

 the Tertiary are the apparently sudden ap- 

 pearance, all over the world, of placental 

 mammals, ending, if the deposits are truly 

 Pliocene, with the Java Pithecanthropus, 

 and at the beginning of the Quaternary 

 with paleolithic man. 



The question here arises as to what re- 



* The Eelation between Base-leveling and Organic 

 Evolution, referring to J. T. Guliok's article in Proo. 

 Boat. Soc. Nat. Hist., XXIV., 1870, pp. 166-7. 



tarded the progress in the mammalian 

 types, although small, generalized, feeble 

 insect-eaters had originated certainly in the 

 Triassic and probably as early as the end 

 of the Permian. We can only account for 

 it by the unfavorable biological environ- 

 ment, by the apparently overwhelming 

 numbers of Mesozoic reptiles, adapted as 

 they were for every variety of station- 

 and soil, whether on land, in the ocean,, 

 in the lakes and rivers, and even in the air. 



When the reptiles became partly extinct' 

 a great acceleration in the evolution of 

 mammals at once resulted. There were 

 now upland grassy plains, bordered by ex- 

 tensive forests, which also clothed the high- 

 lands, and all the geographical conditions- 

 so favorable to mammalian life became pro- 

 nounced after the Cretaceous seas were^ 

 drained off. 



In his admirable essay on the relation 

 between base-leveling and organic evolu- 

 tion, which we had not read until after 

 planning and writing this address, though 

 following the same line of thought, Mr. J. 

 B. Woodworth suggests that mammalian, 

 life in the Mesozoic was unfavorably af- 

 fected by the peneplain and by reptilian 

 life. 



" The weak marsupials or low mammals, 

 which appear in this country with Droma- 

 therium in the tolerably high relief of the 

 Trias, were apparently driven to the up- 

 lands by the more puissant and numerous 

 reptilia of the peneplain. Their develop- 

 ment seems also to have been retarded."' 

 Again he says : " To sum up the faunal 

 history of the Mesozoic alone, we have seen 

 that pari passu with the creation of broad! 

 lowlands there was brought on to the stage 

 a remarkable production of reptiles, a 

 characteristic lowland life ; and we note 

 that the humble mammalia were excluded 

 from the peneplain or held back in their 

 development, so far as we know them bj' 

 actual remains, during this condition of" 



