Aug 1ST 17, 18S3.] 



SCIENCE. 



191 



cliules mind as well as matter. On the other hand, 

 without being absDiiitc idealists, we may hold that 

 mind is more potent than matter, and nearer to 

 the real essence of things. Our science is in any 

 case necessarily dualistic, being the product of the 

 reaction of mind on nature, and must be largely 

 subjective and anthropomorphic. Hence, no doubt, 

 arise much of the controversy of science, and nmch 

 of the unsolved difficulty. We recognize this when 

 we divide science into that which is experimental, 

 or depends on apparatus, and that which is observa- 

 tional and classiticatory, — distinctions, these, which 

 relate not so much to the objects of science as to our 

 methods of pursuing thoni. This view also opens 

 up to us the thought ihat the domain of science is 

 practically boundles*: for who can set limits to the 

 action of mind on the universe, 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, 

 ami resign ourselves to the confession of inevitable 

 ignorance, tt becomes us, rather, boldly to confront 

 the uns'ilved questions of nature, and to wre.-tle with 

 their difficulties till we master such as we can, and 

 cheerfully leave those we cannot overcome to be 

 grappled with by our successors. 



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

 your attention to those transcendental questions 

 which relate to the ultimate constitution of matter, 

 the nature of the ethereal medium filling space, the 

 absolute difference or identity of chemical elements, 

 the cause of gravitation, the conservation and dissipa- 

 tion of energy, the nature of life, or the primary ori- 

 gin of bioplasmic matter. I may take the uuich more 

 humble role of an inciuirer into the unsolved or 

 partially solved problems which meet us in consider- 

 ing that short and imperfect record which geology 

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

 which leads no farther back than to the lime when a 

 solid rind had already formed on the earth and was 

 already covered with an ocean. This record of geol- 

 ogy covers but a small part of the history of the earth 

 and of the system to which it belimgs, nor does it 

 enter at all into the more recondite problems in- 

 volved; still it forms, I believe, some necessary prep- 

 aration, 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 an- 

 swered in many and discordant ways; yet the leading 

 elements of the answer may be given very simply. 

 The oldest rock formation known to geologists is the 

 lower Laurentian, the fundamental gneiss, the Lew- 

 isian formation of Scotland, the Ottawa gneiss of 

 Canada. This formation of enormous thickness 

 corresponds to what the older geologists called the 

 fundamental granite, — a name not to be scouted, 

 for gneiss is only a strati6ed 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 crystal- 

 line, and having for its dominant ingredient the 



mineral orthoclase, — a compound of silica, alumina, 

 and potash, — in which are embedded, as in a paste, 

 grains and crystals of quartz and hornblende. We 

 know very well, from its texture and composition, that 

 it cannot be a product of mere heat; and, being a bed- 

 ded rock, we infer that it was laid down layer by 

 layer, in the manner of aqueous deposits. On the 

 other hand, its chemical composition is quite differ- 

 ent from that of the muds, sands, and gravels usually 

 deposited from Wiiter. Their special characters are 

 caused by the fact that they have resulted from the 

 slow decay of rocks like these gneisses, under the 

 operation of carbonic acid and water, whereby the al- 

 kaline matter and the more soluble part of the silica 

 have been washed away, leaving a residue mainly sili- 

 ceous and aluminous. Such more modern rocks tell 

 of dry land subjected to atmospheric decay and rain- 

 w.ash. If they have any direct relation to the old 

 gneisses, they are their grandchildren, not their ptir- 

 ents. On the contrary, the oldest gneisses show no 

 pebbles, or sand, or limestone — nothing to indicate 

 that there was then any land undergoing atmospheric 

 waste, or shores with sand and gravel. For all that 

 we know to the contrary, these old gneisses may have 

 been deposited in a shoreless sea, holding in solution 

 or suspension merely what it could derive from a 

 submerged crust recently cooled from a state of fusion, 

 still thin, and exuding here and there through its 

 fissures heated w.aters and volcanic products. 



It is scarcely necessary to say that I have no con- 

 fidence in the supposition of unlike composition of 

 the earth's mass on different sides, on which Dana 

 has partly based his theory of the origin of conti- 

 nents. The most probable conception seems to he 

 that of Lyell ; namely, a molten mass, uniform except 

 in so far as denser material might exist toward its 

 centre, and a crust at first approximately even and 

 homogeneous, and subsequently thrown into great 

 bendings upward and downward. This (jiiestion has 

 recently been ably iliscussed by Mr. C'ro^by in the 

 London Geolo'jicnl mwjazineA 



In short, the fundamental gneiss of the lower Lau- 

 rentian m.ay have been the first rock ever formed; 

 and in any case it is a rock formed under conditions 

 which have not since recurred, except locally. It 

 constitutes the first a1id best example of these clienii- 

 co-physical, aque(uis or aqueo-igneous rocks, so ch.ar- 

 acteristlc of the earliest period of the earth's history. 

 Viewed in this way, the lower Laurentian gneiss is 

 probably the oldest kiiul of rock we shall ever know, 

 — the limit to our backward progress, beyond which 

 there remains nothing to the geologist, except physi- 

 cal hypotheses respecting a cooling, incandescent 

 globe. For the chemical conditions of these primi- 

 tive rocks, and what is known as to their probable 

 origin, I must refer you to my frietyl Dr. Sterry 

 Hunt, to whom we owe so much of what is known 

 of the older crystalline rocks,'- as well .-is of their lit- 

 erature and the questions which they raise. My 

 purpose here is to sketch the remarkable difference 

 which we meet as we ascend into the midtlle and 

 upper Laurentian. 



' June, 18s3. ' Hunt, Ki<8ay» un clivniicul geology. 



