GEOLOGY. 259 



edge lias been extended. A few of the leading events in the foregoing 

 history of the growth of conception are worthy of special distinction : 



First in importance, by reason of its broad philosophic bearing, must 

 bo mentioned the transition from a purely objective or empiric chissifi- 

 cation in geology to the more logical, simple, compreheusive, and nat- 

 ural chissification by processes or by fundamental principles and laws — 

 a transition commeuced some years since, but now so well advanced as 

 to be a legitimate subject of permanent record. 



Second in importance must be ranked the birth of the New Geology, 

 which interprets geologic history from the records of degradation as the 

 old geology interpreted history from the records of deposition, and thus 

 greatly extends the domain of the science. 



Next in importance must be placed the invention of a method of de- 

 termining the depth of earthquake centers and the determination of 

 the velocity of earthquake transmission, which together have not only 

 revolutionized seismology and placed it upon a solid foundation, but 

 have enlightened geologists as to the constitution of the sub-crust of 

 the earth. These three steps in progress are epoch-marking, and the 

 last in particular must be credited wholly to the biennial period just 

 closed. 



Important place must be given to the recognition and definition of 

 a great geologic group — the Algonkian — by which the known geologic 

 column is greatly extended and known geologic history greatly ex- 

 panded. Like this discovery in kind are the recognition of a sub-group 

 of rocks corresponding to a part of the geologic column — the Lower 

 Cretaceous — hitherto recognized in Europe, but not on the American 

 continent, and the correct determination of the succession of the sub- 

 ordinate divisions of the Silurian and Cambrian in the structurally 

 complex and bitterly contested field beyond the Hudson. To the stu- 

 dent of stratigraphy these events are epoch-marking. 



Turning now from the subject matter of the science and the growth 

 of knowledge with respect to this subject matter, and toward the means 

 by which the science is developed, another epoch marking event ap- 

 pears in the organization of the Geological Society of America, by 

 which investigation will inevitably be stimulated and knowledge ad- 

 vanced more rapidly than ever before; and in the same category must 

 be placed the establishment of a national geologic periodical, the Ameri- 

 can Geologist. And the birth of State geologic surveys in Arkansas 

 and Texas must also be mentioned. 



Many other notable steps have been taken with respect both to the 

 means and the ends of geology; but even if there were none other these 

 great strides would render the period 1887, 1888 memorable. 



