644 THE POPULAR SCIENCE MONTHLY. 



cal and physical — which work in and upon them, and we must see 

 how they work. 



As I have already said, the early geologists had full faith in 

 the importance of their labors, but they were forced to abandon 

 them by a lack of methods and appliances suitable to cope with 

 the difficulties presented. To-day this importance is not dimin- 

 ished, but rather increased, by what has been accomplished along 

 other lines. If we can renew the attack upon the old questions 

 with improved weapons, the rewards of victory are as promising 

 as ever. It is believed that such weapons are now in our hands, 

 and the hope of success is almost daily attracting fresh and ear- 

 nest workers to the ranks from every land. 



The first and strongest impetus to a renewed study of the 

 rocks themselves was given by the successful application of the 

 microscope to this end ; but this most valuable acquisition has by 

 no means remained alone in the rapid growth of modern petrogra- 

 phy. Other appliances, scarcely less useful in rock-study, fol- 

 lowed quickly in its wake. Microchemical analysis, the separat- 

 ing funnel, and, most of all, the furnace, in which has been accom- 

 plished the perfect synthesis of many rocks, have all contributed, 

 along with the microscope, to make the methods of petrography 

 not inferior in delicacy and accuracy to those of any other 

 science. 



The greatest difficulty with which the older geologists had to 

 contend, in their studies of the rocks, was their inability to iden- 

 tify the constituent minerals which composed them. Their disap- 

 pointment and vexation are still curiously recorded in some of our 

 oldest rock-names, like " dolerite," deceptive ; and " aphanite" not 

 apparent or distinguishable. With the successful application of 

 the microscope to rock-study, this difficulty at once disappeared, 

 and at the same time new and unexpected problems of the great- 

 est interest unfolded themselves in quick succession. 



In the light of all that had been done with the aid of the 

 microscope in the organic sciences, it may at first seem strange 

 that its application to geology was so long delayed. This was 

 due to the imaginary difficulties in preparing transparent rock- 

 sections, and to the fact that rock powders had been examined 

 microscopically at an early date with absolutely no result. 



In spite of certain sporadic efforts in this direction, it was not 

 until the year 1858 that the clew to the solution of the difficulty 

 was hit upon by Henry Clifton Serby, a wealthy manufacturer 

 of Sheffield, England, who as a pastime succeeded in making 

 transparent rock-sections. These he examined with the micro- 

 scope with good results, but the matter would hardly have re- 

 ceived serious attention by scientific men had he not, almost by 

 accident, transplanted his idea to Germany. In this congenial 



