252 RECORD OF SCIENCE FOR 1887 AND 1888. 



transformed from the clastic or ainorplions to the crystalline form ; min- 

 eral veins and ore deposits result from alterations dne to heat, pressure, 

 and other conditions; gases are set free in the processes of alteration of 

 original sediments, and are sometimes accumulated in the rocks in great 

 volume ; and so a large share of those geologic phenomena which are 

 of general economic interest result from processes of alteration of the 

 rocks of the earth. The products of many of these processes belong 

 rather to lithology and chemistry, or to the arts, than to geology; but 

 some of them fall within the legitimate field of the latter science. 



Several years ago E. W. Hilgard proposed a classification of the soils 

 of certain Southern States by the conditions of their genesis ; but cir- 

 cumstances prevented the application of this classification to the soils 

 of the country at large. During the past year Powell has adopted and 

 extended this genetic classification of soils, and proposes to apply it to 

 the entire country. Thus tiir the classification and the plan for its ap- 

 plication has been published only in brief;* but it may be added that 

 soil investigation has already been commenced in several divisions of 

 theU. S. Geological Survey, and that a number of soil maps have been 

 prepared and are shortly to be published. Agricultural geology is the 

 geology of the future; and although great progress in the study and 

 classification of soils has not yet been made, it is of interest to note 

 that the work has been definitely commenced <lnring the biennial period, 

 and that important results will doubtless soon appear. 



Two notable events in geologic progress during recent years are (1) 

 the discovery by Becker that enormous masses of crystalline rocks in 

 the Sierra Nevada Mountains, hitherto supposed to be Archean, are, 

 instead, matamorphosed sediments of Cretaceous age ; and (2) the elu- 

 cidation of the genesis of the iron ores of the Lake Superior region by 

 Irving and Van Hise; but these events primarily belong rather to the 

 domain of lithology than geology. 



In the history of the subjugation of natural forces for human weal 

 there is no more interesting episode than that of the utilization of the 

 unstable carbon compounds as fuels aiul ilUaninants. Wood and vari- 

 ous woody i)lants have been used as fiu'l, and animal fats aiul vegetal 

 oils as illuininants from time immemorial; and there is scarcely a 

 savage tribe to which they are unknown. The advance from the use 

 of wood and charcoal to the burning of mineral coals was an easy one, 

 and was probably made gradually and independently in many centers 

 both during historic and prehistoric time. The last step in the utiliza- 

 tion of potential energy stored up in mineral substances was far longer 

 and was taken within our own memory ; and, in consequence of the 

 ready communication of recent years between distant lands, was taken 

 in many parts of the world at about the same time. It is true that 



* Science, ISi^B, vol. xii, p. 150. 



