Mat 13, 1910] 



SCIENCE 



739 



Dr. Arthur O. Lovejoy, of the IJniversity 

 of Missouri, has been appointed professor of 

 philosophy at the Johns Hopkins University. 



The J. PiEEPONT Morgan professorship in 

 biology at Trinity College, made vacant by 

 the resignation of Dr. Charles Lincoln Ed- 

 wards, has been filled by the appointment of 

 Max Withrow Morse, Ph.D. (Columbia), of 

 the College of the City of New York. Dr. 

 Morse will take charge of the work in Sep- 

 tember. The second professorship in the de- 

 partment, held by Karl Wilhelm Genthe, Ph.D. 

 (Leipzig), who returns to Prussia, will not be 

 filled at present. 



In the Harvard Medical School, Dr. W. E. 

 BrinekerhofE, who for the past four years has 

 been a member of the U. S. Government 

 Leprosy Investigation Commission at Molokai 

 Island, has been appointed assistant professor 

 of pathology, and Dr. S. B. Wolbach, at pres- 

 ent director of the pathological laboratory of 

 the Montreal general hospital, has been ap- 

 pointed assistant professor of bacteriology. 



Dr. H. W. Morse has been appointed to an 

 assistant professorship of physics, and Dr. L. 

 J. Henderson to an assistant professorship of 

 biological chemistry at Harvard University. 



Dr. K. T. Fischer, of the Munich School 

 of Technology, has been called to a chair of 

 physics in the University of La Plata. 



DISCUSSION AND CORRESPONDENCE 



THE STUDY OF ROCKS WITHOUT THE USE OF THE 

 MICROSCOPE 



The phrase " without the use of the micro- 

 scope " appears on the title page of two well- 

 known text-books of petrography.' In a num- 

 ber of colleges and universities there are 

 petrography or lithology courses given in 

 which rocks are treated entirely from the 

 megascopic standpoint. The writer has no 

 fault to find with the two excellent text-books 

 mentioned, for they may be used in connection 

 with microscopic work; but he does take issue 

 with the method of studying rocks without the 

 microscope. 



* Kemp, " Handbook of Rocks " ; Pirsson, " Rocka 

 and Rock Minerals." 



In order to anticipate our critics, let us as- 

 sume at the outset that the average student 

 has neither the time nor inclination to be- 

 come an expert petrographer and also that in 

 after life he will not have a polarizing micro- 

 scope available. In view of these facts why 

 then should the microscope be used in the 

 study of rocks? 



In the writer's opinion no one can have an 

 adequate knowledge of rocks imtil he has 

 studied them in thin sections. What con- 

 ception of the gradations between rocks, the 

 variations in texture, intergrowths, inclu- 

 sions and alterations has the student who has 

 never made a microscopic study of rocks? 

 Yet some idea of these things is essential to 

 an understanding of rocks. What does he 

 know about fine-grained rocks such as basalts 

 or the fine groundmass of such rocks as rhyo- 

 lites? After the student has studied a type 

 collection of rocks, together with the corre- 

 sponding thin-sections, he is in a position to 

 determine the commonly occurring rocks in 

 hand-specimens because he has worked out 

 thin-sections of similar rocks. In studying 

 the slides he looks for minerals in the hand- 

 specimen that would otherwise escape his 

 notice, and learns to identify them. He has 

 also developed his imagination and can in 

 some measure predict what minerals the rock 

 contains. He will be pretty certain, for ex- 

 ample, if the phenocrysts in a porphsrritie 

 rock are quartz, that the fijie groundmass is a 

 mixture of quartz and orthoclase. A heavy, 

 black, fine-grained rock, he knows, is almost 

 sure to consist of plagioelase, augite, mag- 

 netite and more or less glassy base. Black 

 prismatic phenocrysts are either augite or 

 hornblende or possibly a rare pyroxene or 

 amphibole. Of course the student will make 

 mistakes; even experienced petrographers are 

 not infallible. One advantage of the micro- 

 scopic study is that the student realizes the 

 limitations of sight determination. The 

 added interest and knowledge of rocks gained 

 more than compensates for the time taken 

 up with a short study of optical mineralogy. 

 The lack of time will be the objection raised 

 against my plan, but whatever the time avail- 



