LESSONS IN GEOLOGY. 



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VOCABULA 



EXERCISE 55. GREEK-ENGLISH. 

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EXERCISE 56. ENGLISH-GREEK. 



1. Old ape is very burdensome. 2. Nothing is swifter than 

 thought. 3. Moderation is the safest. 4. No bird is blacker 

 than the raven. 5. The boy is swift, the man is swifter, the 

 horse is swiftest. 6. Youth is more attractive than old age. 

 7. The Ethiopians are very black. 8. No one of the Athenians 

 was more self-controlled than Socrates. 9. Critias was more 

 given to plunder (robbing) than Alexander. 10. Nothing ia 

 more pleasing than beautiful flowers. 





LESSONS IN GEOLOGY. III. 



GEOLOGICAL AGENTS RAIN SPRINGS WELLS. 

 HAVING given a general idea in the last chapter of the appear- 

 ance which stratified and unstratified rocks present, we proceed 

 to answer the natural question, What causes have contributed to 

 the composition of these rocks, and by what means have they 

 been placed in their present positions ? 



We shall confine our attention first to the stratified rocks. 



These rocks owe their existence to aqueous action. A casual 

 acquaintance with their appearance is sufficient to indicate this ; 

 but as we proceed wo shall find that they contain, in a fossil 

 state, innumerable remains of animal and vegetable life ; and that 

 these are so universally the remains of marine and aquatic life, 

 that when the fossil of a land animal or a bird is discovered, it 

 is considered a rare exception to the rule. No other proof is 

 required beyond this of the fact that stratified rocks were 

 once sediment, deposited at the bottom of seas and lakes ; in 

 the course of their accumulation, shells, dead fish, occasionally 

 the body of a land animal brought down by a river, sea-weeds, 

 corals, etc., became embedded in the sediment, and by processes, 

 to be described in due time, impressions were taken of them in 

 the matter of the deposit then being made, and they are pre- 

 sented to us as fossils, a word which is derived from the Latin 

 /bssus, " dug up." 



This action is now going on, and there is no reason for be- 

 lieving that it has ever varied, but that existing causes have 

 been the agents by which all the stratified rocks have been pro- 

 duced. 



Geologists have only lately arrived at this conclusion. At 

 first sight, many facts soem to oppose it. For when the fossi- 

 iiterous strata are arranged in chronological order that is, 

 when they are piled one above the other in the order in which 

 they were deposited the series does not, as we might expect, 

 present a gradation of rocks gradually passing from one mineral 

 nharacter to another, and containing animal and vegetable 



remains, which indicate slow change* of speoiM, bat we ptsc 

 directly from highly inclined strata to systems resting horizon 

 tally upon them from rooks of one mineral compot-r 

 those of a totally different character from an wwembla^e of 

 organic remains in one stratum, to find in iU neighbour imme- 

 diately above it a world of life well nigh totally distinct, and 

 only possessing a few species in common with it. These facto 

 were understood to indicate that the surface of the earth had 

 been subject to catastrophes, which overwhelmed the existing 

 orders of life. Thene periods of disorder were succeeded by 

 ages of repose, during which the usual order of things con- 

 tinued, new strata were deposited on the shattered and upheaved 

 crnnt, and now species of life aroite from the wreck of the over- 

 thrown world. But do the observed facts demand such a theory 

 for their explanation? Suppose, for example, that Wales 

 where the oldest stratified rocks are developed, the Silurian 

 was now submerged, and upon the present land a deposition of 

 sediment was made, in which specimens of the various animals 

 now living in the Irish Channel were fossilised ; and suppose 

 that, in process of time, the upheaving force lifted the ocean- 

 bed, and it became again dry hind, whose surface was studied 

 by the then existing race of geologists : what would be the facts 

 which presented themselves ? A series of strata reposing hori- 

 zontally upon rocks of a distinct mineral character, which were 

 highly inclined ; the fossils of the upper rocks being utterly 

 distinct from those of the lower. Would they then be warranted 

 in coming to the conclusion that when the period of the depo- 

 sition of the Silurian had come to an end, a mighty convulsion 

 upheaved the strata, killed all existing life, and that a new 

 creation peopled the seas with new types of life ? We see how 

 erroneous such a speculation would be. 



The student must bear in mind a few prominent truths, which 

 we shall illustrate, from facts observation has procured. 



1. That no rocks can be formed on dry land. Hence the sur- 

 face of the earth may be divided into areas of deposition and 

 of non-deposition. 



2. That in the making of rocks no new matter is used ; it is 

 only a re-arrangement of materials already in existence. 



3. That the material deposited in one place represents the 

 degrading action which has taken place in another. 



4. That at all times there have been continents and seas, for 

 in every class of rocks wo have fossil evidence of the existence 

 of land ; and that the wearing down of the continents has been 

 the chief source of the sediment deposited upon the ocean- 

 bed. 



5. That the earth's crust has from all time been subject to 

 local upheavings and subsidings, which have now caused the 

 ocean-bed to become dry land, and now the dry hind to be sub- 

 merged. Thus, with the exception of those localities where 

 the primary rocks lie exposed, the whole surface of the earth 

 has alternately served as " an area of deposition," or of " non- 

 deposition." And even with regard to the primary rocks which 

 now form tho surface, we cannot declare positively that they 

 never were submerged, for they may have been covered with 

 sedimentary strata which has subsequently been washed off; 

 though this may generally be decided by the appearance of the 

 face of the rock. These are tho main principles which observa- 

 tion of existing causes has enunciated. Wo shall treat of these 

 causes in tho order of their observation, taking the most im- 

 portant agent first. 



THE GEOLOGICAL ACTION OP WATER. 



Rain. The atmosphere is capable of holding in solution a 

 vast quantity of water. When its temperature is raised, this 

 capability of holding moisture is greatly increased ; on the 

 other hand, if by any cause its temperature be decreased, the 

 moisture it contains first condenses into clouds ; and if the tem- 

 perature fall still lower, the minute globules of which the clouds 

 are composed coalesce into drops, and descend to the earth as rain. 



The amount of water thus suspended in the firmament above 

 us is beyond our conception. A thunder shower even has been 

 known to pour down upon a limited area as much as 200,000 

 tons of water in a few hours. 



The fall of rain varies with localities. In the equatorial 

 regions Humboldt calculates that 93 inches fall annually. Here 

 the great solar heat causes the distillation of the ocean-waters 

 to be carried on with vigour. At a latitude of 45, the rain-foil 

 is only 29 inches; and 15 further north, 17 inches. In th>> 



