Jan., 1917J The Future For Geologists 91 



Harkcrj says: "A systematic treatment of igneous rocks on 

 the lines of ])ctrogenesis is not to be expected in the immediate 

 future. " 



One attempt has been made to correlate remote igneous 

 rock sections, viz., between Scandinavia and the Adirondacks. 

 When we know enough of petrogenesis we may be able to 

 correlate volcanic rocks pretty generally even as we do 

 sedimentaries. 



Concerning metamorphic rocks we cannot yet tell in many 

 instances whether the specimen was made from sedimentary 

 or from igneous rocks, and until methods for making such 

 identification are found many stratigraphic and regional 

 petrographic problems remain unsolved. And until we under- 

 stand much more than at present of both igneous and meta- 

 morphic rocks we shall be in the dark on the nature of the 

 earth's interior. Right here some day, however, as suggested 

 above, we may look for important light on cosmic geology. 



8. In the field of Economic Geology have been gleaned 

 many facts. This is particularly true in connection with some 

 of the richer ore deposits and especially in the United States, 

 Europe and some English and German possessions. It is very 

 difficult to say what more there is to learn in this field until more 

 progress has been made in areal and petrographic geology. 

 It certainly is true, however, that in three-fourths of the land 

 surface of the earth but little is known regarding its deposits of 

 mineral wealth. Discoveries of new and valuable deposits 

 have been made with at least the usual frequency right down 

 to date, and there is no reason to believe that we are near the 

 end of such discoveries. They may reasonably be expected 

 to continue for hundreds of years as our exploration of the 

 stratigraphy continues over the rest of the earth, first in tem- 

 perate zones. North and South, then in equatorial regions the 

 w^orld around, then in the high latitude lands, and finally 

 as exploration of the igneous rocks is also prosecuted in all lati- 

 tudes and longitudes. 



Moreover, new uses may be found by geologist, chemist, or 

 manufacturer for substances now neglected or little used, and 

 the geologist must then explore for the deposits of the newly 

 desired substances. There is, I believe, a great field for inven- 

 tion in the combinations of metals and semi-metals, and in the 



fHarker, A., Natural History of Igneous Rocks, Page 376. 



