392 Transition Bocks of North America, 



are elongated, so as to form a pointed pencil ; but when their pile is old 

 and worn, they are of a much ligliter tint, greyish-brown or reddish- 

 brown above, and the lighter colour of the sides is not then so contrasted 

 "with the darker colour of the back. 



{To he continued in our next Number.) 



Transition Bocks {Paloeozoic Rocks of Messrs Rogers) of North 



America. 



The following interesting document is extracted from an 

 address delivered at the meeting of the Association of ximeri- 

 can Geologists and Naturalists, on May 4. 1844, by Professor 

 H. D. Rogers. It contains a short account of the order of 

 succession, and some of the characters of the different North 

 American transition formations, from the deepest or oldest, 

 called Primal, which rests upon certain sandstones or quartz 

 rocks (one of them called Potsdam sandstone), and conglome- 

 rates without petrefactions, which may be considered as the 

 uppermost deposits of the primitive class. To those reading 

 on American Geology, this sketch will prove very useful. The 

 nomenclature part of the extract does not harmonise with our 

 views on this subject. 



We propose to distribute the whole great body of strata 

 from the base, that is, from the Potsdam sandstone, and the 

 conglomerates, to the top of the coal measures in nine distinct 

 series, the products of as many great successive periods ; and 

 resorting to the analogy between these periods and the nine 

 natural intervals into which the day is conveniently divided, 

 we have named them in ascending order, the primal, matinal^ 

 levant, premedidial, medidial, post-medidial, ponent, wspertine, 

 and serai series, the deposits of the dawn, morning, sunrise, 

 forenoon, afternoon, sunset, evening, and twilight periods of 

 the Great Appalachian Palaeozoic day. Subdividing eaoh series 

 in obedience to natural and obvious relations of the organic 

 remains and mineral boundaries, we have named each ultimate 

 subdivision or formation, calling the time during which each 

 formation was produced an epoch ; and between the series and 

 formations, we have constructed groups, in all cases where the 

 natural affinities of the formations require that two or more 

 of these latter shall be united into associations, subordinate 

 to the series. 



Our Primal series embraces the four great rooks between 



