828 THE POPULAR SCIENCE MONTHLY. 



We recognize this when we divide science into that which is experi- 

 mental, or depends on apparatus, and that which is observational and 

 classificatory distinctions, these, which relate not so much to the ob- 

 jects of science as to our methods of pursuing them. This view also 

 opens up to us the thought that the domain of science is practically 

 boundless ; for who can set limits to the action of mind on the uni- 

 verse, or of the universe on mind ? It follows that science must be 

 limited on all sides by unsolved mysteries ; and it will not serve any 

 good purpose to meet these with clever guesses. If we so treat the 

 enigmas of the sphinx Nature, we shall surely be devoured. Nor, on 

 the other hand, must we collapse into absolute despair, and resign our- 

 selves to the confession of inevitable ignorance. It becomes us, rather, 

 boldly to confront the unsolved questions of Nature, and to wrestle 

 with their difficulties till we master such as we can, and cheerfully 

 leave those we can not overcome to be grappled with by our suc- 

 cessors. 



Fortunately, as a geologist, I do not need to invite your attention 

 to those transcendental questions which relate to the ultimate consti- 

 tution of matter, the nature of the ethereal medium filling space, the 

 absolute difference or identity of chemical elements, the cause of gravi- 

 tation, the conservation and dissipation of energy, the nature of life, 

 or the primary origin of bioplasmic matter. I may take the much 

 more humble role of an inquirer into the unsolved or partially solved 

 problems which meet us in considering that short and imperfect record 

 which geology studies in the rocky layers of the earth's crust, and 

 which leads no further back than to the time when a solid rind had al- 

 ready formed on the earth and was already covered with an ocean. 

 This record of geology covers but a small part of the history of the 

 earth and of the system to which it belongs, nor does it enter at all 

 into the more recondite problems involved ; still it forms, I believe, 

 some necessary preparation, at least, to the comprehension of these. 



What do we know of the oldest and most primitive rocks ? At 

 this moment the question may be answered in many and discordant 

 ways ; yet the leading elements of the answer may be given very sim- 

 ply. The oldest rock formation known to geologists is the lower 

 Laurentian, the fundamental gneiss, the Lewisian formation of Scot- 

 land, the Ottawa gneiss of Canada. This formation of enormous 

 thickness corresponds to what the older geologists called the funda- 

 mental granite a name not to be scouted, for gneiss is only a stratified 

 granite. Perhaps the main fact in relation to this old rock is that it 

 is a gneiss ; that is, a rock at once bedded and crystalline, and having 

 for its dominant ingredient the mineral orthoclase a compound of 

 silica, alumina, and potash in which are imbedded, as in a paste, 

 grains and crystals of quartz and hornblende. We know very well, 

 from its texture and composition, that it can not be a product of mere 

 heat ; and, being a bedded rock, we infer that it was laid down layer 



