TKOGEESS OF GEOLOGIC THEORY 319 



cognises sundry minor ones : as those of glaciers and ice- 

 bergs ; those of coral-polypes ; those of Protozoa having 

 siliceous or calcareous shells — each of which agencies, insig- 

 nificant as it seems, is found ca])able of slowly working 

 terrestrial changes of considerable magnitude. Thus, then, 

 the recent progress of Geology has been a still further de- 

 parture from primitive conceptions. Instead of one cata- 

 strophic cause, once in universal action, as supposed by 

 Werner — instead of one general continuous cause, antago- 

 nized at long intervals by a catastrophic cause, as taught 

 by Hutton ; we now recognize several causes, all more or 

 less general and continuous. We no longer resort to hy- 

 pothetical agencies to exj^lain the phenomena displayed by 

 the Earth's crust; but we are day by day more clearly per- 

 ceiving that these phenomena have arisen from forces like 

 those now at work, which have acted in all varieties of 

 combination, through immeasurable periods of time. 



Having thus briefly traced the evolution of geologic 

 science, and noted its present form, let us go on to observe 

 the way in which it is still swayed by the crude hypotheses 

 it set out with ; so that even now, old doctrines that are 

 abandoned as untenable in theory, continue in practice to 

 mould the ideas of geologists, and to foster sundry beliefs 

 that are logically indefensible. We shall see, both how 

 those simple sweeping conceptions with which the" science 

 commenced, are those which every student is apt at first to 

 seize hold of, and how several influences conspire to main- 

 tain the twist thus resulting — how the original nomencla- 

 ture of periods and formations necessarily keej)S alive the 

 original implications ; and how the need for arranging new 

 data in some order, naturally results in their being thrust 

 into the old classification, unless their incongruity with it is 

 very glaring. A few facts will best prepare the way for 

 criticism. 



