INTRODUCTION. «T 



An approximate measurement of all the strata along the Appalachian 

 chain gives an aggregate thickness of forty thousand feet, while the 

 same formations in the Mississippi valley measure scarcely four thou- 

 sand feet ; in this, also, are included the Carboniferous limestones, 

 which do not exist in any eastern section. 



In the Mississippi valley we have numerous points where the Lower 

 Silurian strata are exposed, and at some points there is a thickness of 

 five hundred feet of the Potsdam sandstone. From this base we follow 

 the series upwards to the top of the mounds, capped by the Niagara 

 limestone ; and we there attain an elevation above the Mississippi 

 waters of one thousand feet, which is the whole thickness of the forma- 

 tions from the Potsdam sandstone to the Niagara limestone. The actual 

 measurement of the same set of strata in the Appalachian region would 

 give us more than sixteen thousand feet ; and even making large allow- 

 ances for excess in the measurements, we certainly have, in the Appa- 

 lachians, more than ten times the thickness of the entire series in the 

 west. Still we have no mountains of this altitude ; that is to say, we 

 have no mountains whose altitude equals the actual vertical thickness 

 of the strata composing them. 



In the west there has been little or no disturbance, and our highest 

 elevations of land mark essentially the aggregate thickness of the strata 

 which produce the elevation. In the east, though we prove step by 

 fltep that certain members of the series, with a known thickness, are 

 included in these mountains, the altitude never reaches the aggregate 

 amount of the formations. Reasoning from the facts adduced, and with- 

 out prejudice or theory, the result certainly does not agree with our anti- 

 cipations ; for on the one hand, we find in a country not mountainous, 

 elevations corresponding essentially to the thickness of the strata; 

 while in a mountainous country, where the strata are immensely 

 thicker, the mountain heights bear no comparative proportion to the 

 thickness of the strata. 



We have seen that one simple and intelligible sequence of strata, 

 from the Potsdam sandstone to the end of the Coal measures, covers, 



