Trof. T. Sterry Hunt — Elements of Primary Geology. 497 



These yarions cases, it is evident, introduced certain apparent 

 perturbations into the normal order of crenitic rocks, and should be 

 carefully borne in mind. The many evidences of the displacement 

 of previously formed crenitic rocks, alike in rigid masses, and in a 

 softened and plastic condition, are especially worthy of a critical 

 study. A more careful investigation than has generally been made 

 alike of the chemical, mineralogical, and geognostical history of the 

 various silicated rocks, keeping in view all of the above considerations, 

 will, it is believed, serve to cori'ect some of the extreme views 

 of certain geologists of the metamorphic school, as well as those 

 of the plutonists. 



11. The process of mineral evolution seen in the succession of 

 the earlier and later indigenous crenitic rocks, and in the veinstones 

 or endogenous rocks of still later periods, has continued, though with 

 progressively diminished activity, through Palaeozoic and still later 

 ages down to the present time, as evidenced by the indigenous 

 silicates sometimes found in Palaeozoic rocks, and even in the 

 deep-sea ooze and the deposits of certain thermal waters. The 

 transition from the earliest fundamental granite to the predomi- 

 nantly uncrystalline sediments of the Palseozoic age is marked 

 by gradations, so that it is not easy to define the respective limits of 

 what were originally designated Primary, Transition, and Secondary 

 rocks. The tei-ms Azoic, Eozoic, and Paljeozoic, are for a different 

 reason equally vague. While organic life undoubtedly existed long 

 before what is called Palasozoic time, we have no evidence that it 

 had appeared when the fundamental granite, that is to say, the basal 

 granitoid gneiss, was laid down ; although it is apparent that the 

 formation of certain crystalline silicates was still active in later 

 Transition times, contemporaneous with organic life. 



A failure to grasp this conception has led geologists of the 

 Huttonian school to an undiscriminating use of the vague and ill- 

 defined term metamorphism, which, in the interest of a more exact 

 science, it would be well to banish from the language of geology. 

 The extremists of that school have maintained, and still maintain, 

 that the chemical and mineralogical constitution of the crenitic silico- 

 aluminous rock-masses has no constant and definite relation to their 

 age, and that large areas of Secondary sediments have, by a subse- 

 quent metasomatic change, been converted into mineral masses un- 

 distinguishable from the crystalline strata of the earlier Primary 

 periods. Without referring to the fact that recent and careful 

 geognostical studies have at every point shown the fallacy of the 

 stratigraphical evidences adduced in favour of this assumption, it may 

 be remarked that the whole metamorphic hypothesis is an attempt to 

 substitute a constant intervention of miracle for the orderly and 

 systematic evolution which appears in the mineralogical history of 

 the earth's crust. 



The transition above referred to introduces a difficulty into our 

 terminology, since among the crenitic indigenous masses are included 

 both Eozoic rocks and others which are apparently pre-Eozoic. Both 

 the Primary and the Transition of Werner are also included therein. 



DECADE III. VOL. IV. — NO. XI. 32 



