STRATIFIED AND UNSTRATIFIED ROCKS. 69 



groups, and very often form their axis or nucleus. Stratified rocks fill 

 the plains and form the encircling flanks of the mountains. "When a 

 vast mass of unstratified rock, as granite, forms the nucleus of a 

 mountain group, the stratified materials which surround it generally 

 slope away on all sides, as if the granite had been protruded from 

 below these strata, and, during the act of its uplifting, had broken 

 them and caused them to assume their several inclinations. Other 

 unstratified rocks, as basalt and porphyry, appear amongst the stratified 

 and bedded rocks, sometimes in irregularly lenticular masses, as if 

 they had been spread in a melted state around a common centre, some- 

 times filling long vertical fissures in the strata, as if they had been 

 injected from below. 



Mineral Characters. On comparing together the stratified and 

 unstratified rocks, we find their mineralogical composition extremely 

 different. The stratified rocJcs are earthy aggregates, as sandstones, 

 clays, or limestones; such materials, in fact, as we know to be 

 accumulated in the same mode of arrangement by modern waters ; 

 and in a majority of cases we shall find that most if not all of the 

 stratified rocks are non-crystalline. 



The umstrcdified rocks, on the other hand, are generally and evidently 

 crystallised masses, often analogous to igneous or volcanic products, or 

 compounds containing essentially minerals which are not known to be 

 producible from water, but in several instances are obtainable by arti- 

 ficial heat, or generated in the deep furnaces of which volcanic moun- 

 tains are the vents ; and the greater number of the crystalline rocks 

 are unstratified or have no true bedded structure. These generalisa- 

 tions will have their exceptions, some rocks being bedded and crys- 

 talline as well, their crystalline nature or condition having been 

 subsequently induced, or they were originally non-crystalline. 



Stratified rocks have evidently been deposited successively from 

 above ; the lowest first, the uppermost last, in obedience to the laws 

 of deposition. 



Unstratified rocks, on the other hand, seem to be derived from 

 below or at depths in the earth's interior, and to have been ejected or 

 uplifted from below the superincumbent strata, as volcanic matter is 

 protruded at the present day, or they may have occurred as lava- 

 flows, or as volcanic ashes, terrestrial in origin. 



Contents. Stratified rocks contain very generally the remains of 

 plants and animals which were in existence at the period when the 

 rocks were deposited or accumulated, exactly as remains of the 

 present races of plants and animals are found buried in the modern 

 deposits formed in water. All such remains are termed fossils, hence 

 the stratified rocks are termed fossiliferous and the unstratified rocks 

 unfossiliferous, and in nearly every instance a non-crystalline rock is 

 fossiliferous. 



But unstratified rocks contain no such evidences of aqueous origin 

 or mechanical aggregation, and they rarely possess organic remains 

 except when volcanic ashes or mud have entombed the life of the 



