26 THE EAETH FORMED. 



old ; that is, their verges rest at an angle against the sides of 

 the senior formation. These new rocks are again, in their 

 turn, broken up and placed in high inclinations by new and 

 similar upbursts of igneous rock ; so as to become liable, of 

 course, to similar disintegration. Such a repetition of wearings 

 down and raisings up, implying frequent changes of land and 

 sea, has been in reality the history of our globe since it took 

 its present shape. A granitic crust, containing vast and pro- 

 found oceans, as is proved by the extent and thickness of the 

 earliest strata, was the infant condition of the earth. Points 

 of unconformableness in the overlying aqueous rocks, connected 

 with protrusions of granites, and other similar presentments 

 of the internal igneous mass, such as trap and basalt, mark 

 the conclusions of subsequent sections in this grand tale. 

 Dates, such as chronologists never dreamed of compared with 

 which those of Egypt's dynasties are as the latter to a child's 

 reckoning of its birthdays have thus been presented to the now 

 living generation, in connexion with the history of our planet. 

 The aqueous rocks, taken in their details, are a vast number. 

 Geologists, however, group them in formations or systems, partly 

 with reference to their lithological characters and the breaks 

 in stratific arrangement above described, and partly with regard 

 to an entirely different class of particulars. It is now time to 

 say that, from an early portion of the sedimentary rock series 

 to its close, the mineral masses are found to enclose remains 

 of the organic beings (plants and animals) which nourished 

 upon earth during the time when the various strata were 

 forming ; and these organisms, or such parts of them as were 

 of sufficient solidity, have, in many instances, been preserved 

 with the utmost fidelity, although for the most part converted 

 into the substance of the enclosing mineral. Now, as we pass 

 along through the series of strata, we find a cessation of certain 

 specific forms of plants and animals, while others come to 

 view ; at some points, the change is almost complete at 

 others, it is very considerable. Such demarcations are taken 

 into account by geologists in the grouping of the rock series. 

 They speak of a Palceozoic Period (EaXcuoc, ancient, faov, an 

 animal), comprehending a large early section, terminating at 

 a point where the specific forms are for the first time almost 

 wholly changed ; a Secondary Period, and a Tertiary Period, 

 these also giving groups of species all but distinct. Under 

 each period are reckoned certain systems, more or less or- 

 ganically distinct, and these we shall now proceed to treat 

 separately. 



