OS XORTIl AMERICAN ZOOIOGY. 125 



tains there is an immense longitudinal valley extending from 

 the x\rctic sea to the Gulf of Mexico, crossed by no dividing 

 ridges of note, but forming three separate water-sheds; the 

 southerly one having, in addition to a general easterly declina- 

 tion to the Mississippi, also a descent from the 49th parallel 

 towards the outlet of the latter river in the Gulf of Mexico ; 

 tlie northerly one having an inclination towards the Arctic sea, 

 commencing between the 53rd and 54th degrees of latitude 

 and the central one, which is necessarily the most elevated, 

 having merely an easterly descent towards Hudson's Brj- The 

 valley or plain is widest beween the 40th and 50th parallels, 

 where it includes 15 degrees of longitude. This configuration 

 of the land evidently gives great facilities for the range of 

 herbivorous quadrupeds from north to south, and is the line of 

 route piu'sued by many species of migratory birds ; and while 

 the Mackenzie furnishes a channel by which the anadromous 

 fish of the xVrctic sea can penetrate 10 degrees of latitude to 

 tiie southward, the Mississippi oifers a route by which those 

 of the Gulf of Mexico can ascend far to the north. 



There are no mountain chains to the eastward of the Missis- 

 sippi at all approaching to the Rocky Mountains in magnitude, 

 the most remarkable of the existing ones being the AUeghanies or 

 Apalachian ranges, which have a breadth of about one hundred 

 miles, and rise from 2000 to 3000 feet above the sea, springing 

 from a base elevated 1000 or 1200 feet. Tliey extend from Ala- 

 bama and the northern confines of Georgia nearly to the banks 

 of the St. Lawrence, their general direction being about N.E. 

 by N., that is, nearly parallel to a line drawn from Carolina to 

 Nova Scotia through the principal promontories of the Atlantic 

 coast, and forming an angle of five points with the Rocky Mount- 

 ain chain. The strip of country intercepted between the Al- 

 leghanies and the Atlantic, undulating and rising moderately to- 

 wards the base of the mountains and generally very level near 

 the coast, has a width of 200 miles in the Carolinas. In Georgia 

 the low land becomes broader, and sweeping to the westward 

 round the south end of the chain it joins the valley of the 

 Mississippi. To the southward the level is continued into the 

 peninsula of Florida, and this tongue of land must be noticed 

 as influencing the distribution of animal life, not oidy by its 

 southerly extension, amounting to five degrees of latitude, but 

 also by its forming a barrier to the direct passage of fish from 

 the Atlantic coast to the same parallel in thebottom of the 

 Gulf of Mexico, and thus partly accounting for the very peculiar 

 ichthyology of the Mississippi and its tributaries as contrasted 

 with that of the eastern rivers. 



