1028 HISTORICAL GEOLOGY. 



by all that has since come to light, and Geology now has, as regards North 

 America, a record of the chief consecutive events in a continuous process of 

 development. It has become manifest also that the development has gone 

 forward not simply by enlargement about a nucleus, but through successive 

 stages of work in Interior seas, having, in general, Archaean confines ; and 

 that the great Interior Continental sea was not due to a return to oceanic 

 conditions, but a phase in this endogenous feature in the method of progress. 

 Europe also had its interior seas, and Asia, — ^the two almost one; and so 

 also had Australia, for the later facts show that in Cretaceous, or Cretaceous 

 and Tertiary time, the Australian continent was divided in two by such interior 

 waters. An exception to the general principle has been made by putting a 

 hypothetical continent in the Indian Ocean. But the facts suggesting the 

 hypothesis have been shown to be explained otherwise. 



A detailed review, in this place, of the steps in the process of develop- 

 ment is not necessary. The closing pages of the Dynamical Geology, 391 

 to 396, are an appropriate continuation of these remarks on the earth's 

 development. With regard to the hypothesis on page 396, respecting the 

 alternate or zigzag arrangement of the continents, geological history affords 

 no satisfactory testimony. There is only the interesting fact that the ore 

 belt along the Andes of South America is continued through the nearly east 

 and west bend of Central America to the Eocky Mountains and extends on 

 northward to Wyoming, with remarkable similarity in its ores and the age 

 of the veins. Whether the supposed continental displacement gave this 

 displace nieiit to the deep-seated ore region that in the earth's later eruptive 

 periods supplied the ore ; or whether the similar position of the ore veins 

 was due simply to a like position of the two continents with reference to 

 the Pacific oceanic basin, it is not safe to say. 



Details with regard to continental development have been given in the 

 chapters on Geographical and Geological progress, closing the accounts of the 

 Lower Silurian (page 524), the Paleozoic (page 714), the Mesozoic (page 

 867), and the Tertiary (page 932). 



PROGRESS IN THE EARTH'S LIFE. 



General principles with regard to the jyr ogress in the earth's life. — The 

 Animal aiid Vegetable Kingdoms studied by science comprised, not very 

 long since, only living species. Through the revelations of geology they 

 now include, in addition, the life of an indefinite succession of faunas 

 through the past ages up to, if not over, the borders of Archaean time. As 

 a consequence of these developments, the following principles were early 

 announced with respect to the progress in the earth's life : — 



I. Progress from aquatic life to terrestrial life, commencing in the waters 

 in an era of nearly universal waters, and reaching its higher stages over the 

 land. 



