182 Louis Valentine Pirsson. 



ment in attractive form, appealing specially to their 

 imagination, as by giving them a clear connected outline 

 of the more essential facts of earth history arranged in 

 the logical order of the science. Or, as Professor Schu- 

 chert has expressed it, — ' ' To undergraduates Pirsson was 

 a good teacher, holding them not by picturesque or fas- 

 cinating language, but by his knowledge of his subject 

 and his clear and fluent presentation of it. ' ' 



Nearly twenty years ago Pirsson and his colleague, 

 Charles E. Beecher, planned a text book in geology for 

 undergraduates, but the death of the latter in 1904 pre- 

 vented the execution of the plan. Some years later, in 

 collaboration with Professor Schuchert, the plan for a 

 "Text-book of Geology" was revived and the work was 

 published in 1915. The success of the book has been 

 notable. Some 15,000 copies of the "Physical Geology" 

 part of this text book have been sold and a thoroughly 

 revised edition, which the author completed but a few 

 months before his death, is about to appear. It may be 

 of interest to record the origin of one feature of the 

 "Physical Geology" which illustrates the logical meth- 

 ods of the author, while the success of the book seems to 

 indicate the soundness of his judgment on an important 

 point in text books. 



When planning the book Pirsson examined a consider- 

 able number of corresponding text books by well-known 

 authors, with the object of ascertaining the relative 

 weights which different men had given to different 

 branches of the subject, as represented by space. He 

 found that every author gave a disproportionate amount 

 of space to his own specialty. Disregarding this special 

 branch of each work he secured an average weight 

 assigned by the authors in question to the principal 

 topics, aside from the one in which prejudice had been 

 displayed. Pirsson thought that the proper balance of 

 treatment would be more nearly secured by accepting 

 such an average than by using his own judgment. And 

 this average was adopted for his Physical Geology. 



The Text-book was planned for the undergraduate and 

 Schuchert tells of Pirsson's repeated injunction that the 

 geologist's desires or needs must not be allowed to in- 

 fluence the presentation. 



Pirsson's aim to adapt his presentation to the needs of 

 a particular group was further illustrated by the text 

 book "Rocks and Rock Minerals," intended to meet the 



