TERRESTRIAL PHENOMENA. 147 



of finely-pulverized mineral bodies, covered with layers of the 

 siliceous shields of infusoria, and with transported soils con- 

 taining the bones of fossil animal forms of a more ancient 

 world. The study of the strata which are so differently formed 

 and arranged before our eyes, and of all that has been so vari- 

 ously dislocated, contorted and upheaved by mutual compres- 

 sion and volcanic force, leads the reflective observer, by 

 simple analogies, to draw a comparison between the present 

 and an age that has long passed It is by a combination of 

 actual phenomena, by an ideal enlargement of relations in 

 space, and of the amount of active forces, that we are able to 

 advance into the long sought and indefinitely anticipated do- 

 main of geognosy, which has only within the last half century 

 been based on the solid foundation of scientific deduction. 



It has been acutely remarked, " that notwithstanding our 

 continual employment of large telescopes, we 'are less ac- 

 quainted with the exterior than with the interior of other 

 planets, excepting perhaps our own satellite." They have 

 been weighed, and their volume measured : and their mass 

 and density are becoming known with constantly-increasing 

 exactness, thanks to the progress made in astronomical ob- 

 servation and calculation. Their physical character is, how- 

 ever, hidden in obscurity, for it is only in our own globe that 

 we can be brought in immediate contact with all the elements 

 of organic and inorganic creation. The diversity of the most 

 heterogeneous substances, their admixtures and metamor- 

 phoses, and the ever-changing play of the forces called into 

 action, afford to the human mind both nourishment and enjoy- 

 ment, and open an immeasurable field of observation, from 

 which the intellectual activity of man derives a great portion 

 of its grandeur and power. The world of perceptive pheno- 

 mena is reflected in the depths of the ideal world, and the 

 richness of nature and the mass of all that admits of classifica- 

 tion, gradually become the objects of inductive reasoning. 



I would here allude to the advantage of which I have 

 already spoken, possessed by that portion of physical science 

 whose origin is familiar to us, and is connected with our 

 earthly existence. The physical description of celestial 

 bodies, from the remotely- glimmering nebulaB with their 

 suns, to the central body of our own system, is limited, as we 

 have seen, to general conceptions of the volume and quantity 



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