Prof. Rogers's Address, fyc. 247 



Art. III. 



Naturalists 



of the Association of 



1844 ; by Henry D. Rogers, I 

 of Pennsylvania, F. G. S., &c. 



(Concluded from p. 160.) 



MESOZOIC PERIOD. 



the 



Let us now take a brief survey of the state of our knowledge of the 

 mesozoic formations of this country, or those produced during what 

 may be termed the middle ages of geological history. The vast inter- 

 val between the remote epoch of our coal and the dawn of the existing 

 marine species in the eocene tertiary, is much more imperfectly repre- 

 sented in North America than either the earlier or later periods. With 

 exception of its last or cretaceous age, this great interval, which, in 

 the eastern continent, is so rich in beautiful monuments of extinguished 

 hfe, so abundant in striking records of the physical revolutions of our 

 globe, seems to have left on this side of the Atlantic only a few frag- 

 mentary memorials of its races or its events. Like some of the ob- 

 scurer periods in human mediceval history, these, the dark ages of Amer- 

 lc an geological time, have been explored of late with a zeal and skill 

 a »akened by the very difficulties of the research, and which have al- 

 ready produced some very instructive results. 



Referring the isolated formations of this country, whose dates are 

 ■atermediate between the coal and the tertiary, to the more full and 

 continuous scale of the European strata, as a present standard of com- 

 parison, we are now acquainted with deposits belonging to three distinc 

 ^sozoic epochs, the equivalents severally of the upper new red sand- 

 or Triassic rocks, of the lower oolitic deposits, and of the cretaceous 

 Thus we are destitute, so far as this continent has yet been 

 ex plored, in products of the newer paleozoic period, or, in other words, 

 a ny representatives of the Zechstein or magnesian limestone group of 

 Eur ope, and likewise in equivalents of several of the middle and upper 



°° lltic formations of the old world. 



A concise exhibition of some of the facts bearing upon the determi- 

 nation of the age and origin of the three known mesozoic formations 

 of tn e United States may not be unsuitable on this occasion. 

 Jhe older of these groups of strata, which I shall call the Mesozoic 

 J sandstone, occupies two long and narrow and probably shallow 



t 



stone 

 strata. 



m 



red 



trou ghs, extending along the eastern side of the great Blue Ridge chain 

 m its northeastern prolongation in New Jersey, New York and New 



