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September 20th, 1843. 



Regular meeting — the President in the Chair. 



Dr. Binney read a paper "On the influence of physical 

 causes on the geographical distribution of the genera and 

 species of terrestrial mollusks of the United States." 



In this paper the author first gave a concise description of the 

 great geographical divisions of the territory of the United States, 

 which he divided into the three distinct regions, viz. 



1. The Pacific Region, — that lying between the Pacific Ocean 

 and the Rocky Mountains. 



2. The Central Region, — that between the Rocky Mountains 

 and the Alleghany Mountains, including the whole country watered 

 by the Mississippi River and its tributaries. 



3. The Atlantic Region,— lying between the Alleghany Moun- 

 tains and the Atlantic Ocean. 



He then discussed the question, whether merely geographical 

 features exercised any influence on the distribution of the terres- 

 trial mollusks, and arrived at the conclusion, that unless combined 

 with climatal causes, they offered scarcely any obstacle to their 

 extension. The Rocky Mountains, rising above the limits of per- 

 petual frost and snow, were considered to form an impenetrable 

 barrier ; while the Alleghany Mountains, of moderate elevation, and 

 covered to their summits with forests, were traversed in every direc- 

 tion by these animals, so that the same species are for the most 

 part found on both sides of them. Hence he inferred that the 

 country west of the Rocky Mountains, constitutes a distinct zoolo- 

 gical region, and the country between these mountains and the 

 Atlantic Ocean another. 



The other causes considered were the following : — Climate 

 Elevation, Geological Struclure, Vegetation, Humidity and Dry 

 ness, which were classed as primary and constant causes ; and In 

 undations, Fires, Agriculture, Increase of Domestic Animals 

 Proximity of the Sea, Commercial intercourse with Europe, Ex 

 cessive Heat or Cold of particular seasons, and Oceanic currents 

 which were set down as accidental or secondary causes. After 



