178 Louis Valentine Pirsson. 



by Professor Verrill. In 1894 lie was invited to consider 

 a transfer to Johns Hopkins University as successor to 

 the brilliant teacher of petrology, George H. Williams, 

 but his work had been recognized at the Scientific School 

 and he preferred to accept a promotion to the position 

 of assistant professor of inorganic geology. In 1897 he 

 was promoted to the full professorship in physical geol- 

 ogy, a position he held until his death. 



From the time of his permanent connection with the 

 Sheffield Scientific School, the development of Pirsson's 

 career was rapid in three directions ; first as an investi- 

 gator and author of notable contributions to the advance- 

 ment of geology; second as a teacher and author of text 

 books ; and third in University administration. It seems 

 advisable to consider separately these three phases of his 

 busy and effective life. 



In the field of research Pirsson possessed in fine devel- 

 opment the natural qualifications of a true scientific in- 

 vestigator. He had a keen, logical and philosophical 

 mind, coupled with a lively imagination which he knew 

 how to regulate. His powers of patient accurate obser- 

 vation and of concentrated attention were naturally 

 associated with a highly retentive memory. He was very 

 methodical in his plan of work, from the beginning to the 

 end of every important task. Thus when he came to take 

 up his real life work he was exceptionally equipped. He 

 had a thorough training in physics, chemistry, crystallog- 

 raphy and general mineralogy, and in his skill as an 

 analytical chemist he possessed a tool which was to be of 

 great service. Added to all this was a wonderful store 

 of general knowledge, which was often turned to good 

 account. 



Pirsson's researches fall naturally into a few groups. 

 First come a series of mineralogical papers, some ten in 

 number, representing the results of his two years' work 

 in Penfield's laboratory. These studies were made on 

 specimens collected by himself or placed at his disposal 

 by Professor Brush. They are important as showing 

 how completely he was equipped for such work whether 

 involving the measurement and figuring of complex crys- 

 tals or determining by analysis the chemical composition 

 and discussing the same. After these first two or three 

 years Pirsson did little detailed mineralogical investiga- 

 tion except on constituents of igneous rocks. 



Following his purely mineralogical studies Pirsson 



