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 diminished, 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 earnest 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 petrography. Other appliances, scarcely less useful in rock-study, followed quickly in its wake. Microchemical analysis, the separating funnel, and, most of all, the furnace, in which has been accomplished 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 identify the constituent minerals which composed them. Their disappointment 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 greatest 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 microscope with good results, but the matter would hardly have received serious attention by scientific men had he not, almost by accident, transplanted his idea to Germany. In this congenial