ILL-HEALTH 



the smaller Geology, and later the works on Volcanoes and 

 Coral Islands, besides numerous contributions to the 

 current journals, are the proofs of his unceasing industry. 

 But although unremitting in labor, he was not " inde- 

 fatigable," for weariness from time to time overcame 

 him, and compelled him to take long periods of rest and 

 observe a rigid regimen in respect to exercise and sleep. 

 Of these unfavorable conditions of health the pages of 

 this memoir give many illustrations, but it may be worth 

 while to state, in a single paragraph, the crises through 

 which he went. 



Incessant mental exertion impaired his health when 

 he was about forty-five years old, notwithstanding the 

 orderly quiet and the temperance of his domestic life. 

 The warnings became so serious that at length he deter- 

 mined to go abroad with his wife and try the effect of 

 complete separation from his usual avocations. This 

 journey to Europe extended from October, 1859, to 

 August, 1860, a rest of ten months, of which three were 

 spent in Switzerland. One of the minor fruits of this 

 relaxation was a vade-mecum prepared for the use of 

 students who might wish to see the Alps by a very 

 moderate expenditure of money. 



For some years after his return the powers of the 

 naturalist seemed to be restored, and it was then that the 

 large Manual of Geology and the smaller text-book were 

 made ready for publication, between 1862 and 1864, and 

 the large Mineralogy in 1868. Again he broke down, 

 and his lectures were read to the students by his younger 

 colleague, Professor O. C. Marsh. In 1869-70 he suffered 

 from a severe attack of fever, which completely prostrated 

 him, and from which his recovery was slow. Again in 

 1874, another illness, proceeding from a cold, disabled 

 him for a time. In 1880, he was compelled to seek re- 

 lease from college duties. Then came a decade when his 

 intellectual activity was regulated by the strictest care. 



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