TEOGKESS 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 capable 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 \mivcrsal 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 explain the phenomena displayed by 

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

 ceiving that tli esc 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 keeps 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. 



