66 A CENTUEY OF SCIENCE 



graphic features of the earth were very different from 

 those of to-day. Throughout the Paleozoic, and, less 

 markedly, the Mesozoic, the oceans flooded the lands 

 widely (at times over 60 per cent of the total area), high- 

 lands were inconspicuous, sediments far scarcer, and 

 climates warm and equable throughout the world. High- 

 land conditions, and especially the broadly emergent con- 

 tinents of the present, were only periodically present in 

 the Paleozoic and then for comparatively short intervals 

 between the periods. Therefore rates of denudation, 

 solution, sedimentation, and evolution have varied 

 greatly throughout the geological ages. These differ- 

 ences, however, relate to degrees of operation, and not to 

 kinds of processes; but the differences in degree of 

 operation react mightily on our views as to the age of 

 the earth. 



Geologic time had, for Hutton, no "vestige of a begin- 

 ning, no prospect of an end." In other words, geologic 

 time is infinite. He did not, however, discover a method 

 by which the chronology of the earth could be determined. 



First Important Text-books. In 1822 appeared the 

 ablest text-book so far published, and the pattern for 

 most of the later ones, Outlines of the Geology of Eng- 

 land and Wales, by W. D. Conybeare (1787-1857) and W. 

 Phillips (1775-1828). "In this excellent volume all that 

 was then known regarding the rocks of the country, from 

 the youngest formations down to the Old Red Sandstone, 

 was summarized in so clear and methodical a manner as 

 to give a powerful impulse to the cultivation of geology 

 in England" (Geikie). This book is reviewed at great 

 length by Edward Hitchcock in the Journal (7, 203, 1824). 



To indicate how far historical geology had progressed 

 up to 1822 in England, a digest of the geological column 

 as presented in this text-book is given in the following 

 table, along with other information. 



A text-book writer of yet greater influence was Charles 

 Lyell (1797-1875), whose Principles of Geology appeared 

 in three volumes between 1830 and 1833. This and his 

 other books were kept up to date through many editions, 

 and his Elements of Geology is, as Geikie says, "the hand 

 book of every English geologist" working with the fos- 

 siliferous formations. 



