766 THE JOURNAL OF GEOLOGY. 



There is, however, nothing" among the recent discoveries of the 

 microscope in regard to rocks so surprising as their delicate adjust- 

 ment to their environment. We are accustomed to look upon the 

 masses of our mountains as the very type of what is stationary 

 and eternal ; but in reality they are vast chemical laboratories 

 full of activity and constant change. With every alteration of 

 external conditions or environment, what was a state of stable 

 equilibrium for atoms or molecules ceases to be so. Old unions 

 are ever being broken down and new ones formed. Life in our 

 planet, like life in ourselves, rests fundamentally on chemical 

 action. The vital fluid circulates unceasingly through the arteries 

 of the oceans and the currents of the air ; it penetrates the rocks 

 through the finest fissures and invisible cracks, as the human 

 blood penetrates the tissues between artery and vein, producing, 

 with the help of heat and pressure, like changes in the histology 

 of the globe." 1 



The establishment of these convictions became the ruling 

 motive of his later work. The more important of his petrograph- 

 ical studies include those on the gabbro and diorite in the neigh- 

 borhood of Baltimore ; on the massive rocks of the Cortlandt 

 series in New York ; and on the greenstone schists of the Menom- 

 inee-Marquette region. 



As his interests extended into the broader domain of general 

 geology the scope of his investigations widened, and we find him 

 at work on the petrography and structure of the Piedmont plateau 

 in Maryland, and on the occurrence and distribution of the ancient 

 volcanic rocks along the Atlantic seaboard. His work in coop- 

 eration with others on the geology of Maryland occupied a large 

 share of his time in recent years, and appeared in various editions 

 of the map of the state, the last of which is now in press. 



In recognition of the value of his services to the Johns Hop- 

 kins University he was appointed Professor of Inorganic Geology, 

 in 1892. The same year he was honored by the Geological Soci- 

 ety of London by being made a foreign correspondent. He was 

 one of the judges of award in the department of mineralogy at 



1 Popular Science Monthly, September, 1889, pp. 640-648. 



