222 L. V. Pirsson — Rise of Petrology as a Science. 



Art. VII. — The Rise of Petrology as a Science; 

 by Louis V. Pirsson. 



This chapter is intended to present a brief sketch of the 

 progress of the science of petrology from its early begin- 

 nings down to the present time. The field to be covered 

 is so large that this can be done only in broadest outline, 

 and it has therefore been restricted chiefly to what has 

 been accomplished in America. Although the period 

 covered by the life of this Journal extends backward for 

 a century it is, however, practically only within the last 

 fifty years that the rocks of the earth's crust have been 

 made the subject of such systematic investigation by 

 minute and delicately accurate methods of research as to 

 give rise to a distinct branch of geologic science. It is 

 not intended of course to affirm by this statement that the 

 broader features of the rocks, especially those which may 

 be observed in the field and which concern their relations 

 as geological masses, had not been made the object of 

 inquiry before this time, since this is the very foundation 

 of geology itself. Moreover, a certain amount of investi- 

 gation of rocks, as to the minerals of which they were 

 composed, the significance of their textures, and their 

 chemical composition, had been carried out, concomitant 

 with the growth from early times of geology and min- 

 eralogy. Thus, in 1815, Cordier by a process of washing 

 separated the components of a basalt and by chemical 

 tests determined the constituent minerals. At the time 

 this Journal was founded, and for many years following, 

 the genesis of rocks, especially of igneous rocks, was a 

 subject of inquiry and of prolonged discussion. The 

 aid of the rapidly growing science of chemistry was 

 invoked by the geologists and analyses of rocks were 

 made in the attempt to throw light on important ques- 

 tions. It is remarkable, also, how keen were the obser- 

 vations that the geologists of those days made upon the 

 rocks, as to their component minerals and structures, 

 aided only by the pocket lens. Many ideas were put for- 

 ward, the essentials of which have persisted to the pres- 

 ent day and have become interwoven into the science, 

 whereas others gave rise to contentions which have not 

 vet been settled to the satisfaction of all. At times in 



