SOME UNSOLVED PROBLEMS IN GEOLOGY. 63 



The attempt has lately been made to account for these breaks by 

 the assumption that the geological record relates only to periods of 

 submergence, and gives no information as to those of elevation. This 

 is manifestly untrue. In so far as marine life is concerned, the periods 

 of submergence are those in which new forms abound for very obvi- 

 ous reasons already hinted. But the periods of new forms of land 

 and fresh-water life are those of elevation, and these have their own 

 records and monuments, often very rich and ample ; as, for example, 

 the swamps of the carboniferous, the transition from the cretaceous 

 subsidence to the Laramie elevation, the tertiary lake-basins of the 

 West, the terraces and raised beaches of the pleistocene. Had I time 

 to refer in detail to the breaks in the continuity of life, which can not 

 be explained by the imperfection of the record, I could show at least 

 that nature, in this case, does advance per saltum by leaps, rather 

 than by a slow, continuous process. Many able reasoners, as Le Conte 

 in this country, and Mivart and Collard in England, hold this view. 



Here, as elsewhere, a vast amount of steady conscientious work is 

 required to enable us to solve the problems of the history of life. 

 But, if so, the more the hope for the patient student and investigator. 

 I know nothing more chilling to research, or unfavorable to progress, 

 than the promulgation of a dogmatic decision that there is nothing to 

 be learned but a merely fortuitous and uncaused succession, amenable 

 to no law, and only to be covered, in order to hide its shapeless 

 and uncertain proportions, by the mantle of bold and gratuitous 

 hypothesis. 



So soon as we find evidence of continents and oceans, we raise the 

 question, " Have these continents existed from the first in their pres- 

 ent position and form, or have the land and water changed places in 

 the course of geological time ? " In reality both statements are true 

 in a certain limited sense. On the one hand, any geological map 

 whatever suffices to show that the general outline of the existing land 

 began to be formed in the first and oldest crumplings of the crust. 

 On the other hand, the greater part of the surface of the land consists 

 of marine sediments which must have been derived from land that 

 has perished in the process, while all the continental surfaces, except, 

 perhaps, some high peaks and ridges, have been many times sub- 

 merged. Both of these apparently contradictory statements are true ; 

 and, without assuming both, it is impossible to explain the existing 

 contours and reliefs of the surface. 



In the case of North America, the form of the old nucleus of Lau- 

 rentian rock in the north already marks out that of the finished conti- 

 nent, and the successive later formations have been laid upon the edges 

 of this, like the successive loads of earth dumped over an embankment. 

 But, in order to give the great thickness of the palaeozoic sediments, 

 the land must have been again and again submerged, and for long 

 periods of time. Thus, in one sense, the continents have been fixed ; 



