chap. ix. Recent Elevatory Movements. 275 



teued by the so-called Peruvian dew, the proper elements 

 for this action. We can thus understand the peculiar 

 corroded appearance of the shells on San Lorenzo, and 

 the great decrease of quantity in the carbonate of lime 

 in the powder on the upper ledge. There is, however, 

 a great difficulty on this view, for the resultant salts 

 should be carbonate of soda and muriate of lime ; the 

 latter is present, but not the carbonate of soda. Hence 

 I am led to the perhaps unauthorised conjecture (which 

 I shall hereafter have to refer to) that the carbonate of 

 soda, by some unexplained means, becomes converted 

 into a sulphate. 



If the above remarks be j ust, we are led to the very 

 unexpected conclusion, that a dry climate, by leaving 

 the salt from the sea-spray undissolved, is much less 

 favourable to the preservation of upraised shells than 

 a humid climate. However this may be, it is interest- 

 ing to know the manner in which masses of shells, 

 gradually upraised above the sea-level, decay and finally 

 disappear. 



Summary on the recent Elevation of the West 

 Coast of South America. — We have seen that upraised 

 marine remains occur at intervals, and in some parts 

 almost continuously, from lat. 45° 35' to 12° S., along 

 the shores of the Pacific. This is a distance, in a. north 

 and south line, of 2,075 geographical miles. From 

 Byron's observations, the elevation has no doubt extended 

 sixty miles farther south ; and from the similarity in 

 the form of the country near Lima, it has probably 

 extended many leagues farther north. 1 Along this 

 great line of coast, besides the organic remains, there 

 are in very many parts, marks of erosion, caves, ancient 



- i I may take this opportunity of stating that in a MS. in the 

 Geological Soc. by Mr. Weaver, it is stated that beds of oysters and 

 other recent shells are found thirty feet above the level of the sea, 

 in many parts of Tampico, in the Grulf of Mexico. 



13 



