Louis Valentine Pirsson. 183 



need of the mining engineer and geologist alike, for a 

 simple classification and nomenclature for rocks applic- 

 able in the field on megascopic examination. This book 

 has been widely used. 



Pirsson had long projected in his mind a text book 

 of petrology for advanced students. He gave a great 

 deal of thought to the plan of this work which had many 

 original features. It was to cover the broad field of the 

 origin, composition, texture and classification of igneous 

 rocks, and express the author's judgment, after thirty 

 years of experience, as to the best method of teaching this 

 difficult subject. Perhaps a third of the book had been 

 prepared in its first draft. It is greatly to be regretted 

 that it can never be finished, though certain chapters 

 may be found adapted to publication. 



A very considerable number of well-known geologists, 

 teachers, and mining engineers have received a large part 

 of their training in physical geology and petrology from 

 Professor Pirsson. Among these is a notable group of 

 members of the United States and Canadian Geological 

 Surveys. Pirsson 's students were always impressed 

 with his extensive, accurate knowledge of his subject and 

 found him a master of clear, concise statement, yet patient 

 in the explanation of difficult points. He was keen to 

 perceive the individual student's weaknesses and quick 

 with help to remedy them. Remembering a lack in his 

 own early training he paid special attention to instruc- 

 tion in the best habits and methods of research and to 

 instilling into advanced students the high ideals of the 

 seeker after truth which were so prominent in his own 

 character. He was himself "uncompromising with the 

 facts of a problem in hand" and laid wholesome stress 

 upon this principle. 



A trait of much influence which was highly appreciated 

 was the sincere, kindly and truly friendly interest Pirsson 

 always exhibited in the progress of a student's work. 



Professor Pirsson was not only an investigator of high 

 rank and a successful teacher, but his interest in and 

 understanding of the broad problems of University ad- 

 ministration were such as to make him a most valuable 

 officer of the Sheffield Scientific School. This phase of 

 his career has been so happily described by his long time 

 friend and colleague, Professor Chittenden, that it is a 



