Prof. Rogers's Address, ^c. 247 



Art. hi. — -Address delivered at the Meeting of the Association of 

 American Geologists and Naturalists, held in Washington, May^ 

 1844 ; by Henry D. Eogers, Professor of Geology in the University 

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



(Concluded from p. 160.) 



MESOZOIC PERIOD. 



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 

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

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

 life, 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 medioeval history, these, the dark ages of Amer- 

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

 awakened 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 

 intermediate 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 distinct 

 mesozoic epochs, the equivalents severally of the upper new red sand- 

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

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

 explored, in products of the newer pateozoic period, or, in other words, 

 in any representatives of the Zechstein or magnesian limestone group of 

 Europe, and likewise in equivalents of several of the middle and upper 

 oolitic 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 the United States may not be unsuitable on this occasion. 



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

 red sandstone, occupies two long and narrow and probably shallow 

 troughs, extending along the eastern side of the great Blue Eidge chain 

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



