2 INTRODUCTION. 



land, are in truth only working at different stages of one 

 great story." ^ 



In Geology, as in Human History, we desire to go back to 

 the beginning, and here we must discriminate between fact 

 and hypothesis, as we do between actual record and tradition. 

 When we turn to the earliest phases of our Earth's history, or 

 to that branch of the subject termed Cosmogony, we enter 

 the region of hypothesis. Following Laplace, we dimly 

 picture a nebulous mass of intensely heated gaseous matter 

 from which, in process of time, the Solar system was de- 

 veloped. And we conclude that the Earth, like other planets, 

 assumed its present form by gradual cooling, a process which 

 led to various combinations of the elementary substances. 

 At one time a molten sphere surrounded by vapours and 

 gases, the crust at length became solidified ; and when the 

 temperature was sufficiently reduced, the earliest oceanic 

 areas were formed by condensation of the steam and alkaline 

 vapours that previously encircled the Earth. Thus the salt- 

 ness of the sea to some extent dates from the earliest times, 

 although it is partly owing to the saline matter continually 

 carried into it by rivers.^ 



The facts of Geology enable us to discuss the changes 

 which the Earth has undergone since the earliest divisions of 

 land and water were marked out. But until the principles of 

 Geology were established, the ideas concerning the Earth's 

 past history were little more than conjecture. It was clear 

 that various rocks or earths occurred in different areas ; clay 

 in one place, slate in another, chalk here and coal there. 

 Organic remains known as fossils were found in them, and 

 their resemblance to living forms was admitted ; but for a 

 long time they were thought, either to be freaks of Nature, or 

 the products of a Universal Deluge. Thus fossils were ob- 

 served by the early Greek and Roman philosophers, and, 

 many centuries later, by other European students. In our 

 own country, in the seventeenth century. Plot, Lhwyd, and 

 Lister gave accounts of the ' petrifactions ' known to them ; 

 while in the eighteenth century John Woodward published 

 his celebrated "Attempt towards a Natural History of the 

 Fossils of England" (1729), and his collection subsequently 

 formed the nucleus of the Woodwardian Museum. 



That most of the rocks are arranged in layers or strata, was 



^ Address, Somerset Arch. Soc. xxvi. 8. 



- D. Forbes, G. Mag. 1867, p. 438 ; T. S. Hunt, Q. J- xv. 491. See also J. 

 Murray (Brit. Assoc. 1885), Nature, Oct. 15, 18S5, p. 583. 



