PRELUDE TO DESCRIPTIVE GEOLOGY. 537 



here speaking of the formation of a science; and 

 that it is not a collection of miscellaneous, un- 

 connected, unarranged knowledge that can be 

 considered as constituting science; but a metho- 

 dical, coherent, and, as far as possible, complete 

 body of facts, exhibiting fully the condition of the 

 earth, as regards those circumstances which are the 

 subject-matter of geological speculation. Such a 

 Descriptive Geology is a pre-requisite to Physical 

 Geology, just as Phenomenal Astronomy necessarily 

 preceded Physical Astronomy, or as Classificatory 

 Botany is a necessary accompaniment to Botanical 

 Physiology. We may observe also that Descriptive 

 Geology, such as we now speak of, is one of the 

 classificatory sciences, like Mineralogy or Botany; 

 and will be found to exhibit some of the features of 

 that class of sciences. 



Since then, our History of Descriptive Geology 

 is to include only systematic and scientific descrip- 

 tions of the earth or portions of it, we pass over, at 

 once, all the casual and insulated statements of facts, 

 though they may be geological facts, which occur 

 in early writers ; such, for instance, as the remark 

 of Herodotus 2 , that there are shells in the moun- 

 tains of Egypt; or the general statements which 

 Ovid puts in the mouth of Pythagoras 3 : 



Vidi ego quod fuerat solidissima tellus, 

 Esse fretum ; vidi factas ex aequore terras, 

 Et procul a pelago conchae jacuere marinae. 



8 ii. 12. 3 Met. xv. 262. 



