ITS UNIFOKMITY. 71 



without this presumption the history of the Past would 

 be an uncertainty and delusion the geologist proceeds to 

 unfold the history of the stratified deposits, tracing back 

 from the silt of yesterday's tide to the first-formed strata ; 

 and this through the lapse of ages for which chronology has 

 no name save "cycles" and "systems" of indefinite dura- 

 tion. Geology is not entitled it dare not, in the spirit of 

 true philosophy, appeal to " abnormal conditions," to "cata- 

 clysms," or to " revolutionary forces," for a solution of its 

 problems. Certain agents may act over certain areas with 

 greater intensity at one period than at another, or may ex- 

 ert themselves, in the varying distributions of sea and land, 

 over wider areas ; still the results are homologous though 

 differing in magnitude, and cannot be ascribed to convul- 

 sion or disorder. Where geology cannot explain, it can at 

 least observe and describe, and this its legitimate culti- 

 vators will ever do, rather than take shelter under the 

 assumption of abnormal conditions in primeval nature. 

 There is ever much more philosophy in honest doubt than 

 in the utmost ingenuity of unsupported assumption. 



" The agencies," we have elsewhere* observed, "that now 

 operate on and modify the surface of the globe ; that scoop 

 out valleys and wear down hills ; that fill up lakes, and 

 estuaries, and seas ; that submerge the dry land, and ele- 

 vate the sea-bottom into new islands ; that rend the rocky 

 crust, and throw up new mountain-chains ; and that influ- 

 ence the character and distribution of plants and animals, 

 are the same in kind though differing, it may be, in de- 

 gree as those that have operated in all time past. The 

 layers of mud, and sand, and gravel, now deposited in our 

 lakes and estuaries, and along the sea-bottom, and gradually 

 solidifying into stone before our eyes, are the same in kind 

 with the shales and sandstones and conglomerates that 

 * A dvanced Text- Book of Geology. 



