THE 



POPULAR EDUCATOR. 



LESSONS IN GEOLOGY. I. 



INTRODUCTION DIVISIONS OF THE SUBJECT PHYSICAL 

 GEOLOGY THE GEOLOGICAL SYSTEMS MINERALOGY 

 AND LITHOLOGY THE SOLAR SYSTEM, ETC. ETC. 



THE derivation of the word Geology (717 [ghee], the earth, and 

 \oyos [log'os], a discourse, or a reasoning) indicates the main 

 direction of the science. It confines its attention to a description 

 of the solid crust of tho earth, and to the elucidation of those 

 forces and causes which have produced tho changes the surface of 

 our planet has undergone. To aid him in his investigation, the 

 geologist needs the aid of tho botanist, the zoologist, the chemist, 

 tho mineralogist, the physicist, and even of the mathematician. 



Although the subject looks formidable to the general reader, 

 it is not only fraught with the deepest interest, but by far its 

 greatest part may be traversed by common sense. Moreover, 

 its study commends itself to all, since it requires no expensive 

 apparatus, nor yet a preparation which all other sciences 

 demand ere the student can enter on their practice. Young 

 and old, gifted with observation, may at once become practical 

 geologists ; and by never passing a stone-heap without an ex- 

 amination, or never leaving a quarry or gravel-pit unsearched, 

 they will soon lay the foundation of a geological cabinet, and be 

 efficient labourers in the extension of geological research. 



Every generation of our race has produced men of inquiring 

 minds, and it is but natural that such men should turn their 

 research to discover the origin of the world we inhabit, espe- 

 cially in tho early times when but few channels were opened 

 along which they were invited to expend the natural vigour of 

 their intellect ; hence, in the earliest records of eastern nations 

 we find theories which attempt to account for the existence of 

 our earth these it ;a unnecessary to dwell' upon. 



It is evident that the only sound mode of procedure is to collect 

 all the information which observation of the various existing 

 phenomena of nature can give ; to search the crust of the earth 

 for any facts which the rocks, their position, their character, their 

 fossil contents, can afford ; to notice the arrangement of conti- 

 nents and seas, the position and directions of mountain chains, 

 etc., and from these letters of the geological alphabet to spell 

 out tho history of our globe. 



Tho history of tho progress of geology, like that of any other 

 science, can furnish many instances of theories built up with- 

 out any facts for foundations ; but as patient research gradu- 

 ally amassed information, these erroneous suppositions were 

 abandoned, and geologists have, from so many warnings, be- 

 come extremely careful of hazarding opinions. The experiences 

 by which wo have been taught not to speculate, though interest- 

 ing and instructive, we cannot record in these pages, as our 

 limited space requires us to attend to facts and the deductions 

 which may be reasonably drawn from them. 



The division of the subject we propose is tho following : 



1. Physical Geology that is, the geological agencies which 

 have worked the various changes in tho surface of our planet, 

 both as to their present existence and as to tho traces of their 

 power which the rocks reveal. 



2. The Geological Systems. As we pass through these, we 

 shall enumerate the fossils the rocks contain, the history of the 

 animal and vegetable life of our globe, and the localities in 

 which the members of these systems appear. 



3. Mineralogy and Lithology. In our last division wo hope 

 to describe the composition of the various kinds of rocks, as 

 well as the physical and chemical properties of tho minerals 

 they contain. 



Before we enter upon the immediate province of geology, it 

 will bo well to consider our position in the universe, and some- 

 what of the character of our world as a globe, noticing the most 



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plausible of the theories yet produced to account for the con- 

 struction of our system, and therefore of our earth. 



The solar system, of which we are one of the members, consist* 

 of the sun and eight planets four of which are very much larger ( 

 than tho earth and a number of very small planets, called aate- 

 roids, which revolve in the space separating the four exterior and 

 larger planets from the interior and smaller ones. The position of 

 the earth is the third from the sun. The earth is accompanied by 

 a moon, which is not the case with any of the other interior 

 planets, whilst tho exterior planets are all attended by satellites 

 Saturn and Uranus by eight, Jupiter by four. All these bodies 

 revolve round tho sun iu the same direction, and all move within 

 a narrow belt. The exterior planets are much lighter than the 

 interior. If the density of water be taken as 1, tho density of 

 the sun will be about 1}; of Mercury, 9J ; of Venus, 5JJ; of 

 the Earth, 5^ ; of the Moon, 3 ; of Mars, 3J ; of Jupiter, 1; 

 of Saturn, ^ ; of Uranus, jgj. 



The sun's magnitude is immense, as may be judged by the 

 fact that if he were a hollow shell, and the earth placed at tho 

 centre, there would be sufficient room for the moon to revolve, 

 as she now does, at 240,000 miles from tho earth, and there 

 would still be some 200,000 miles beyond tho moon ere the shell 

 of the sun were reached. The planets cannot be said strictly 

 to revolve round the sun, but the sun and the planets revolve 

 about the centre of gravity of the system ; and, owing to the 

 preponderating bulk of the sun, this centre of gravity lies not 

 far from his own centre. 



In searching for a reeord of the process of creation, we 

 naturally turn our attention to that only Book the human 

 library contains which did not emanate from the mind of man. 

 But the Bible was not written as an instructor in physical 

 science, hence we only find the sacred historian dedicating a few 

 verses to the subject of " the creation of the world." Yet we 

 may rest assured that, although the short notice only touches 

 the prominent points, yet every word is true ; and the more 

 science has discovered, the more has she proved to be the com- 

 mentator and unfolder of the great truths contained in those 

 few words. 



A generation since, geologists were looked upon as the oppo- 

 nents of revealed truth, the friends and abettors of infidels and 

 atheists ; but now we have learnt not to generalise from too 

 few facts, but patiently to explore before pronouncing a definite 

 judgment. The interesting questions, " the development of 

 species " and " the antiquity of man," are to-day in the same 

 position as the questions of " the universality of the deluge " 

 and "tho six periods of creation" at tho close of the last century. 

 But we know in these days nothing of the rancour with which 

 the contest was then carried on. Explorers now in every part 

 of tho world collect information, and every right-minded man 

 rests assured that in the end Scripture will not be contradicted, 

 but confirmed. 



The chief points in the description of the creation given in 

 Genesis will be found to be fairly explained by Laplace's nebular 

 hypothesis, which has been extended to the explanation of the 

 contour of the earth's surface. Tho first fiat of the creation was, 

 " Let there be light." Now we are well aware that light is 

 nothing more than the rapid vibration of an invisible existence 

 called ether ; so that our word " light " in the expression quoted 

 must mean " light-giving matter." This corresponds to the fire- 

 cloud of the hypothesis. All bodies of our acquaintance are 

 capable of existing in a state of vapour. The temperature at 

 which this change of state takes place is so high that the vapours 

 are luminous. Hence the first fiat of creative power called into 

 existence all the matter of which tho solar system is composed 

 in a state of highly luminous vapour. In the expression that 

 " the light was divided from the darkness," there seems to be an 



