Sketch of a Classification of the European Rocks. 29 



The old divisions into primitive, transition, secondary, and tertia- 

 ry, are now admitted by many persons to be founded on an errone- 

 ous view of nature ; yet such is the force of habit, that many geolo- 

 gists, aware of the fallacy of these divisions, still continue to use the 

 terms, and we hear nearly as much as ever of transition rocks. 

 Would it not be imagined by the person first directing his attention to 

 the study of geology, that there were three great marked periods, 

 during each of which rocks of a peculiar character, distinct from 

 each other, were formed, and that there was a transition or passage 

 only between the first and second of these. I appeal to those who 

 have examined rocks in the field, and not merely in cabinets and 

 museums, whether or not the student would entertain correct opin- 

 ions. These divisions may be said to have been made in the infan- 

 cy of the science, and doubdess contributed much to its present com- 

 paratively advanced state ; but it should always be recollected that 

 they were formed from limited observations, and were connected 

 with particular theories, which recent and more accurate observa- 

 tions have shown to be any thing but correct. If it shall be proved 

 that there is an occasional passage between the old tertiary and sec- 

 ondary classes, there would appear to be more or less transition 

 throughout the whole series of the stratified rocks, showing that the 

 term transition, at least, is incorrect. A great mass of evidence is, 

 indeed, in favor of a break at the epoch of the Exeter Red Con- 

 glomerate (Rathe Todte Liegende), resulting from a great derange- 

 ment in the previously existing rocks, and the grinding and rounding 

 of detached portions of them into gravels, which when comparative 

 tranquillity was restored, were deposited in horizontal beds on the 

 disturbed strata. Yet able observers assert, that there is an occa- 

 sional passage of these rocks into the coal-measures, upon which 

 they so commonly rest in an unconformable manner. We have now 

 so many instances of great differences in the mineralogical structure 

 of the same formations, either original or consequent on disturbance, 

 that such structure is no longer a character of importance; and it 

 yet remains to be seen how many of the strata supposed to belong to 

 the primitive class are altered rocks. 



M. Brongniart's division into " Sediment Rocks," would be both 

 natural and useful were it certain where such rocks commenced, 

 and that all those necessarily included in the class were so formed. 

 This division has been much used in France of late, and would ap- 

 pear infinitely superior to the terms secondary and tertiary. 



