22 Proceedings of tlie Ohio State Academx of Science 



places upon their work. Only one who is widely acquainted with 

 foreign literature and work can get away from this limitation. 



The other limitation I find myself under is the difficulty of 

 deciding how the state of knowledge of a science at any one time 

 is to be judged. From the best school texts and from the larger 

 manuals? But these, and especially the former, are oiten some 

 years behind the time, even at the date of their issue. From the 

 views current among the workers in tlie science ? It is not always 

 easy to know what views are current. In many cases matters are 

 in debate, still to be fought out to a conclusion. And if it should 

 be the case that some principle, found later to be of great value, 

 has been published but has not found its way to acceptance by 

 workers in the science, can that principle be counted among the 

 possessions of the science at the time? Twenty-five years ago, in 

 1886, Le Conte's Elements of Geology and Dana's Test-book of 

 Geologv were the common college texts, and Dana's Manual of 

 Geology the only American reference manual, while Geikie's 

 Text-hook of Geology was the leading English text^ It is to these 

 books and to the reports current at that time in the national and 

 state surveys that I go to learn the state of geological opinion. 



Before speaking of the new principles which have found 

 their place in geology in the last quarter-century, it is well to call 

 attention to some facts which show the great growth of the 

 science as a whole ; a growth not peculiar to geology, but 

 paralleled in the other sciences. In many of the colleges which now 

 have separate departments of geology, the teaching of geology 

 was then combined with that of other subjects; and in other col- 

 leges and universities which then had separate departments of 

 geology, these departments have now grown in instructors and re- 

 sources. In many states geological surveys were then in existence 

 and doing good work. This work in most cases has grown, and 

 in some cases new surveys have been started. 



The earlier western surveys of Hayden, Powell and King 

 were replaced by the U. S. Geological Survey in 1879; ^"*^1 the 

 magnificent series of reports published by the survey make 

 America's greatest single contribution to geology. In 1882 the 

 Geological Survey had been directed to prepare a geological map 



