456 



CANNA. GEOLOGY. 



later date, arising from the transportation of the more 

 recent stratified rocks, occurs in nature. 



But the case of the trap conglomerate presents an 

 instance of a breccia formed of transported materials, 

 of a partial nature, and limited to this one division of 

 rocks; a division evidently posterior to some or to 

 all of the secondary strata. This conglomerate, by 

 whatever means indurated, is succeeded by a fresh 

 deposit of solid trap, which is again followed by al- 

 ternations of the same substances, marking a series of 

 periods of which there are no corresponding examples 

 in the strictly stratified and secondary rocks. The trap 

 rocks like the granites and the porphyries are marked 

 by many peculiarities; above all by their independence, 

 their partial distribution, and their intrusion among the 

 stratified substances ; but in nothing more strongly than 

 by this their exclusive appropriation of a set of con- 

 glomerates; an appearance proving in them a series 

 of mechanical changes and a succession of eras in 

 which the other rocks of recent origin do not seem to 

 have participated. 



It is impossible to enter much further into this 

 subject without being bewildered in the regions of con- 

 jecture. It is apparent however, that different formations 

 of trap occur on the surface of the earth, distinguished 

 by difference of character as well as by differences in 

 the relative eras of the rocks among which they have 

 intruded. It may perhaps be reasonably argued that 

 these are parts of one general formation, only diversified 

 in character and situation. But the alternations found 

 in C anna prove that the several formations visible there 

 at least, are as distinct in time as they are in place ; 

 since lapse of ;time is evidently implied in the formation 

 of SL conglomerate. It also follows from the same 

 premises, that these formations are partial ; a fact 

 perhaps generally resulting from the other circumstances 

 tf'h.ich iilif'ji.'l tiie rocks of the trap family ; since the 



