ANNOTATIONS AND ADDITIONS. 37 



they are of considerable extent, as peculiarly apt to cause 

 fevers and other illnesses. Several missionary villages have 

 been deserted or removed elsewhere in consequence of this 

 opinion, which is very widely diffused. Supposing the 

 opinion correct, is such an influence of these flat rocks or 

 laxas to be attributed to a chemical action on the atmo- 

 sphere, or merely to the effect of increased radiation ? 



( 5 ) p. 2. " The Llanos and Pampas of South America, 

 and the Prairies of the Missouri" 



The physical and geognostical views entertained respect- 

 ing the western part of North America have been rectified 

 in many respects by the adventurous journey of Major 

 Long, the excellent writings of his companion Edwin James, 

 and more especially by the comprehensive observations of 

 Captain Fremont. These, and all other recent accounts, 

 now place in a clear light what, in my work on New Spain, 

 I could only put forward as conjecture, on the subject of 

 the mountain ridges and plains to the north. In the 

 description of nature as well as in historical inquiries, 

 facts long remain isolated, until by laborious investigation 

 they are brought into connection with each other. 



The east coast of the United States of North America 

 runs from south-west to north-east, in the same direction as 

 that followed in the southern hemisphere by the Brazilian 

 coast from the river Plate to Olinda. In the two hemi- 

 spheres two ranges of mountains exist at a short distance 

 from the eastern coast; they are more nearly parallel to 



