INTRODUCTION. 69 



Mutton's work was projected upon a plane half a century 

 beyond the recognised geology of his own time. Hutton's 

 audience of geologists had to grow up under other influences 

 than polemical discussions between Neptunists and Plutonists, 

 and had to learn from Hutton himself how to tap the fountain 

 of science at its living source. 



In 1793 a Dublin mineralogist, Kirwan, attacked Hutton's 

 work in ignoble terms, and the great Scotsman, now advanced 

 in years, resolutely determined to revise his work and do his 

 best by it. Valuable additions were made, and the subject- 

 matter brought under more skilful treatment. In 1795 the 

 revised work appeared at Edinburgh, in independent form and 

 in two volumes. It was his last effort. Hutton died in 1797 

 from an internal disease which had overshadowed the closing 

 ypafs of his life. 



The original treatise of Hutton is divided into four parts. 

 The first two parts discuss the origin of rocks. The earth 

 is described as a firm body, enveloped in a mantle of water 

 and atmosphere, and which has been exposed during im- 

 measurable periods of time to constant change in its surface 

 conformation. The events of past geologic ages can be most 

 satisfactorily predicted from a careful examination of present 

 conditions and processes. The earth's crust, as far as it is 

 open to our investigation, is largely composed of sandstones, 

 clays, pebble deposits, and limestones that have accumulated 

 on the bed of the ocean. The limestones represent the 

 aggregated shells and remains of marine organisms, while the 

 other deposits represent fragmental material transported from 

 the continents. In addition to these sedimentary deposits of 

 secondary origin there are primary rocks, such as granite and 

 porphyry, which, as a rule, underlie the aqueous deposits. 



In earlier periods the earth presented the aspect of an 

 immense ocean, surmounted here and there by islands and 

 continents of primary rock. There must have been some 

 powerful agency that converted the loose deposits into solid 

 rock, and elevated the consolidated sediments above the 

 level of the sea to form new islands and continents. 



According to Hutton, this agency could only have been v 

 heat ; it could not have been water, since the Cement J 

 material (quartz, felspar, fluorine, etc.) of many sedimentary ' 

 rocks is not readily soluble in water, and could scarcely have 

 been provided by water. On the other hand, most solid rocks 



