IV PREFACE TO THfi SECOND AND THIRD EDITIONS. 



the shores of the Caspian Sea), falls between the period of 

 publication of the second and third editions. This expedi- 

 tion has contributed materially to the enlargement of my 

 views in all that regards the form of the surface of the earth, 

 the direction of mountain-chains, the connection of steppes 

 and deserts with each other, and the geographical distribution 

 of plants in relation to ascertained conditions of tempera- 

 ture. The long subsisting want of any accurate knowledge 

 on the subject of the great snow-covered mountain-chains 

 which are situated between the Altai and the Himalaya (t. e. 

 the Thian-schan and the Kuen-liin), and the ill-judged 

 neglect of Chinese authorities, have thrown great obscurity 

 around the geography of Central Asia, and have allowed 

 imagination to be substituted for the results of observation 

 in works which have obtained extensive circulation. In the 

 course of the last few months the hypsometrical comparison 

 of the culminating summits of the two continents has almost 

 unexpectedly received important corrections and additions, of 

 which I hasten to avail myself. (Vol. i. pp. 57-58,and 92-93.) 

 The determinations of the heights of two mountains in the 

 eastern chain of the Andes of Bolivia, the Sorata and the 

 Illimani, have been freed from the errors which had placed 

 those mountains above the Chimborazo, but without as yet 



