^s'OTES AJsD QUERIES. 



113 



order of their creation. (The last section is termed paleontology, from pa- 

 laios, ancient, and onta, beings.) 



It is necessary to mention that geology throws no light on the origin of 

 the world, or on the nature and state of the materials occurring beneath 

 its crust, or on its condition anterior to the setting-in of ordinary physico- 

 geographical agencies — those are hypothetical subjects. 



The following are some of the principal geological deductions : — 



1. The rocks forming the known portion of the crust of the earth are 

 of two kinds, as regards the origin of their present condition. One con- 

 sists of masses which have been subject to a high temperature ; and the 

 other of materials deposited by the agency of water. They are respec- 

 tively termed Igneous and Aqueous. Principal Igneous rocks : granites, 

 syenites, porphyries, cliorites, felstone, basalt, obsidian, etc. Principal 

 Aqueous rocks : limestones, sandstone, shale, slatestone, salt, gypsum, 

 marl, chalk, etc. 



2. The formation of Igneous and Aqueous rocks has been going on from 

 an immeasurably remote epoch, and still continues. 



The existence of some kind of Igneous rocks in a refrigerated and con- 

 solidated condition, anterior to the formation of Aqueous deposits, can 

 only be hypothetically assumed. 



3. Certain Igneous rocks, as granites and the like, extend, en masse, 

 below the surface of the earth to unfathomable depths ; and wherever ob- 

 served in contact with Aqueous . ocks, they form the foundation of the 

 latter ; others, as basalts and lavas, have been ejected from great depths ; 

 and they generally occur overspreading other rocks. 



The doctrine of the Igneous origin of granite and alliecl rocks has been 

 much contested of late ; there is little doubt, however, of their having 

 been subject to a high temperature (see 6th deduction). 



4. Aqueous deposits, occurring nearly everywhere, and often several 

 thousand feet in thickness, have been derived from previously existing Igne- 

 ous rocks, or from prior-formed deposits of their own class, through the me- 

 chanical and chemical action of atmospheric agents, springs, rivers, lakes, 

 and seas. In this way, huge mountain-masses have been worn down {de- 

 nuded), and valleys excavated ; while their niaterials have been trans- 

 ported to the mouths of rivers, or disseminated over the bottom of lakes 

 and oceans. The remains of plants, corals, shells, and other organisms 

 {fossils) frequently enter into the composition of Aqueous rocks : some- 

 times beds are entirely made up of such remains. 



5. Aqueous rocks, with few exceptions, have been slowly and gradually 

 deposited in more or less horizontal beds {strata) ; — the order of superpo- 

 sition of the beds being the order of their successive formation ; while 

 their relative position denotes their relative period of deposition in the 

 scale of geological time. 



6. Subterranean heat and heated vapours, in many cases emanating 

 from proximate igneous sources, have frequently penetrated deep-seated 

 Aqueous rocks, producing in them molecular re-arrangements, and a more 

 or less crystalline structure, or a change of chemical composition ; therebj'- 

 obliterating many of their original characters, and otherwise metamor- 

 phosing them. List of Metamorphic rocks : gneiss, mica scjiist, hornblend 

 schist, quartz stone, statuary marble, etc. 



Possibly all known Igneous rocks were originally Aqueous deposits that 

 have been completely melted. 



7. The surface of the earth has repeatedly undergone both slow and ' 

 sudden upheavals and depressions. The former movements have raised 

 wide-spread horizontal beds from the bottom of se^s, often several thou^ 



TOL. Y. Q 



