236 J. C. MERRIAM EARTH SCIENCES, BACKGROUND OF HISTOKY 



discusses the origin and early history of our planet. Geology aiid geog- 

 raphy deal directly with the earth. Paleontology, representing biological 

 history, must go to geology for its record. Anthropology has, as one of 

 its most important phases, the history and origin of man. 



The field of the astronomer, with its myriad bodies of the heavens, 

 presumably represents wide range in stage of development of the stellar 

 systems within our view. Yet, with all our information as to the stages 

 through which these bodies may proceed in their evolution, there is but 

 little positive evidence on which we may depend. We may note 

 modifications in the surface of the sun or in the clouds of Jupiter, or we 

 may observe the varying brightness of the stajrs, but there is little in 

 these variations which we can consider as more than incidental fluctua- 

 tion. Our knowledge of evolution of the stellar universe must depend 

 largely upon comparisons of stars of various types, or of groups of stars 

 and nebulae which we assume to represent incipient stellar systems. The 

 nebular hypothesis, which has served as the type of evolution of the solai' 

 system and as a basis for an interpretation of the origin of the earth, is 

 called in question to such an extent as to be no longer acceptable to a, 

 large group of astronomers. The planetesimal hypothesis, developing 

 similar world systems out of spiral nebula?, seems also to suffer under 

 recent criticism. For practical comparisons in study of world evolution, 

 we appear to have one of the most important sources of information in 

 the history of our own planet. For the universe in the large we can prove 

 little more than that there is shown a process of development for which 

 infinite time is required and in which definite cycles are determined. 



Our greatest scientific contributions to study of history and of origins 

 have come through geological and biological investigations. Geology is 

 the greatest of all historical sciences. From comparative and experi- 

 mental studies alone biology makes large contribution, but its distinctly 

 historical phase lies in the field of paleontology, in which the life record 

 is read from the geological book. To geology and biology, furnishing 

 together the life records, anthropological history must be added, reaching 

 back, as it does, into geological history and expressing the beginnings of 

 our account of human life and activity in terms of geology and paleon- 

 tology. 



For the purposes of this paper, geological history may be divided 

 roughly into two portions, one represented in the known section of strati- 

 fied rocks formed through the piling up of sediments and by the out- 

 welling of molten material spread on the surface or squeezed into the 

 strata. An earlier period expresses in a more doubtful manner the partly 



