The Field of Geology— McGee. 191 



ground in an old woodpecker's hole. On rapping on the stub 

 with my gun the bird pushed out its head. The young were 

 of all sizes, showing that the eggs had been incubated from the 

 first laying. The eggs contained large embryos. 



May 8. 1888. ' 



[Papet- y.] 



THE FIELD OF UEOLOGY AJSTD ITS PROMISE FOR THE FUTURE. 



W. J. McGee. 

 I. 



The legitimate field of Geology is now fairly defined, and so 

 fully occupied that it is possible to scan its expanse and discern the 

 tracts yet untrodden by the pioneer. From a survey of the field 

 it appears that many of these lacunae are interesting, and that one 

 is especially noteworthy. 



The primitive geologic classification is based immediately upon 

 phenomena — upon those products of the forces operating naturally 

 upon the earth with which it is the province of the science to deal; 

 but in most cases the processes may be readily inferred from the 

 products, and the phenomena may thus be classified as well by the 

 agencies they represent as by their individual characteristics. So 

 the empiric or formal laws expressing the external relations of the 

 phenomena give place to natural or physical laws expressing their 

 essential relations in terms of the operations by which they are 

 produced; and the ultimate geologic classification thus becomes 

 genetic, or a classification by processes rather than products. 



Now the various processes with which the geologist has to 

 deal fall naturally into two principal and antagonistic categories, 

 which are supplemented and modified by five subordinate categories; 

 and these categories of processes clearly define the province of 

 geology. 



The initial geologic movements (so far as may be inferred 

 from the present condition of the rocks of the earth) were distor- 

 tion or displacement of the solid or solidifying terrestrial crust in 

 such manner as to produce irregularities in the surface of the 

 globe. These are the movements involved in mountain growth 

 and in the development of continents; they have been in operation 

 from the earliest eons recognized by the geologist to the present 

 time; and their tendency is ever to deform the geoid and produce 



