1'20 LECTURES 



miles, or millions of earth radii, so geology her epochs hy millions 

 of years, i. e., earth revolutions. As the astronomer takes the ra- 

 dius of the earth as a base line wherewith to measure the dimensions 

 of the solar system, so the geologist takes the present geological 

 epoch, and " causes now in operation," as a time measuring rod, with 

 which to estimate the length of the tertiary period. As the astrono- 

 mer, becoming more bold as he ascends, takes the diameter of the 

 earth's orbit as a line wherewith to calculate the distances of the fixed 

 stars, or even dares to estimate the probable distance of the remotest 

 nebula, so the geologist, no less daring, takes the tertiary as a rod 

 wherewith to measure approximatively the almost inconceivable lapse 

 of time represented by the secondary rocks, or even dares to cast his 

 telescopic glance back into the dim nebulosity of the remotest palaeo- 

 zoic period. Finally, as the astronomer _, when telescopic vision fails, 

 still speculates, though filled with awe, concerning the infinite, un- 

 known abyss of space beyond, so also the geologist, when mile-stones 

 are no longer visible^ when fossils and stratified rocks fail, still vainly 

 peers with wondering gaze backward, and strives to pierce the dark- 

 ness beyond, still believes that all he sees, or can ever hope to see, is 

 but a fragment of the infinite abyss of time beyond. Overwhelmed, 

 appalled, he shrinks back within himself, and remembers that his own 

 mind, so daring, so arrogant, so apparently limitless, is also but a 

 fragment of the infinite intelligence. 



Thus, while astronomy fills the regions of the universe with objects, 

 geology fills the regions of infinite duration with events. As astronomy 

 carries us upwards by the relations of geometry, geology carries us 

 backwards by the relations of cause and efi'ect. As astronomy steps 

 irom point to point of the universe by a chain of triangles, so geology 

 stej)s trom epoch to epoch of the earth's history by a chain of me- 

 chanical and organical laws. If one depend on the axioms of geome- 

 try, the other depends upon the axioms of causation. In a word, the 

 realm of astronomy is the universe of space, that of geology the uni- 

 verse of time. The one peoples her universe with space-ivorlds , the 

 other her's with creations — time-ioorlds. 



The great object of all science is to establish the universality of law ; 

 harmony in the midst of apparent confusion ; unity in the midst of 

 diversity; unity of force amidst diversity of phenomena, physical sci- 

 ence ; unity of plan in the midst of diversity of expression, natural 

 science. Now, it is the peculiar province of astronomy to establish 

 this universality of law throughout all space^ as it is of geology 

 throughout all time. Astronomy shows that the same force which 

 controls the falling of a stone governs the motions of the heavenly 

 bodies ; so also geology shows that the changes through which each 

 animal passes in its embryonic development are similar to those 

 through which the whole earth and its inhabitants have passed in 

 the course of its geological history; that the same mind which now 

 conducts the one has presided through all time over the other. If 

 astronomy, more than all other sciences, illustrates that sublime attri- 

 bute of Deity, His omnipresence or unchangeableness in space, geology, 

 more than all other sciences, illustrates that other sublime attribute 

 of Deity, His immutability or unchangeableness in time. 



