While there is a large class of tangible and determinate problems of this kind, embracing shiftings of matter on the earth's surface, distortions of strata, and changes of bodily form, there are also problems of a more hidden nature such as internal mutations. These give rise to mathematical, physical, and chemical inquiries while at the same time they call into play the use of the scientific imagination and are thus rich in the possibilities of training. Thus in varied ways geological work joins hands with chemical, physical, mechanical, and mathematical work.
When life first appears in the record, there is occasion to raise the profound question of its origin, and with this arises a closely related question as to the nature of the conditions that invited life, which leads on to the further question, what fostered the development of life throughout its long history? While the obscurity of the earliest record leaves the question of origin indeterminate for the present, duly guarded thought upon the subject should foster a wholesome spirit toward inquiry in this vital line as well as a hospitable attitude toward whatever solution may finally await us. In all such studies the student should be invited to look to _the vestiges left automatically by the process itself_ for the answer, and he should learn to accept the teachings of evidence precisely as it presents itself. So also when a problem is, for the present, indeterminate, it is peculiarly wholesome for the inquirer to learn to rest the case where the light of evidence fails, and to be complacent in such suspension of judgment and to wait further light patiently in serene confidence that the vestiges left by the actuating agencies in their constructive processes are the surest index of the ultimate truth and are likely to be sooner or later detected and read truly.
=Relation of geology to botany, zoölogy, psychology, and sociology=
In the successive records of past life impressed on strata piled one upon another until they form the great paleontologic register, there is an ample and a solid basis for the study of the historic evolution of life. With this also go evidences of the conditions that attended this life progress and that gave trend to it. This record of the relations of life to the environing physical conditions forms one of the most stimulating fields of study that can engage the student who seeks light on the great problems of biological progress. Here geology joins hands with botany and zoölogy in a mutual helpfulness that is scarcely less than indispensable to each.