xxxvi 



had been published previous to my return, 

 in the Connaissance des Temps, and in the 

 Ephemerides of Baron Zach. The trifling 

 differences, which exist between the results 

 obtained by Prof. Oltmanns and myself 

 arise from his having made a more rigorous 

 calculation from the whole of my observa- 

 tions, and his having employed the lunar 

 tables of Burg, and of correspondent ob- 

 servations at Greenwich; while I used only 

 the Connaissance des Temps, calculated 

 from the tables of Masson. 



The observations I had made on the dip 

 of the needle, the intensity of the magnetic 

 forces, and the small horary variations of 

 the variation, will appear in a separate 

 treatise, which will be added to my Essay 

 on Geological Pasigraphy. This last work, 

 which I began to compose in Mexico, in 

 1803, will be accompanied by profiles, in- 

 dicating the stratification and relative age 

 of the rocks, the types of which were ob- 

 served by Mr. Leopold Von Buch and 

 myself in the two continents, between the 

 twelfth of southern and the seventy-first of 

 northern latitude. Aided by the labors of 

 this great geologist, who has examined 



