2 GEOLOGY. 



as through a known system of atmospheric dynamics. We readily 

 follow the growth of an oak back to its origin by reversing its organic 

 processes. By three observations of the apparent positions of a new 

 comet, the astronomer traces its path both backward and forward. 

 In a somewhat similar way, the history of the earth will doubtless in 

 time be traced to its beginning through its dynamical characters. It 

 is quite certain that the earth and the solar system were organized in 

 pursuance of a definite succession of progressive changes which are 

 virtually recorded in the phenomena of the present stage. When a 

 fuller and deeper insight into such phenomena is attained, the record 

 will doubtless become quite readable, and the interpretation sure. 



While awaiting this, we must be content with hypotheses. Since 

 these are our only resource, there is need to form as clear conceptions 

 as possible of those hypotheses that have been or may be entertained, 

 and of their working qualities as applied to the problems of the earth. 

 It is not less important to acquire at the same time a hospitable and 

 intelligent preparedness to appreciate new light as it shall present 

 itself. 



Not a few of the doctrines of geology, when traced back to their 

 ultimate terms, are found to hang on some hypothesis of the earth's 

 initial stage, and to have no greater strength than that hypothesis. 

 It is therefore important to scrutinize these basal hypotheses, to note 

 critically the ways in which they enter into the interpretation of the 

 earth's phenomena, and into the various geological doctrines, and to 

 carry into the study of earth-history a never-failing sense of these 

 hypothetical dependencies. This should serve as a wholesome guard 

 against the acceptance of conclusions as substantiated, when they are 

 in reality hypothetical in their ultimate dependence; especially should 

 it guard against the unconscious acceptance of conclusions as though 

 they were demonstrated, when in reality, traced a step or two backward, 

 they may be found to be grounded solely on a hypothesis. 



It is the glory of geology that it is a growing science. While it 

 has an enormous mass of the firmest data, and its great conclusions 

 rest on most substantial grounds and will never be radically changed 

 by any developments in the future, it has, at the same time, many 

 problems that are yet unsolved, many doctrines that are yet debatable, 

 many depths that are yet unfathomed. At all points, therefore, it 

 invites an investigative spirit: it courts an attitude of independent 



