593 



themselves subject to certain rules, so that the 

 partial changes of direction are most frequently 

 90°, and lead to a total change of * inclination? 

 Is there a parallelism between the direction of 

 the strata and that of the nearest chain of 

 mountains, or has that direction of strata a re- 

 lation with the principal chain, or a very dis- 

 tant oceanic coast ? When we call the assem- 

 blage of rocks of which the strata have the 

 same direction, a loxodromic system of rocks, 

 and when, in a vast country, several of those 

 loxodromic systems touch each other, are the 

 changes of direction always sudden, or are there 

 progressive passages on the limit of contiguous 

 systems? The same soil does not furnish 

 the traveller with the means of answering so 

 great a number of important questions ; but the 

 progress of positive geognosy can only be ad- 



* I allude to the case where, in a chain of mountains of 

 mica-slate-gneiss, the general direction of the strata is hor. 

 4 (from S. W. to N. E.) with the inclination to the N. W., 

 and where the deviations are generally hor. 8 (from S. E. to 

 N. W.) The inclination observed in that inverse direction 

 will not be as it would be towards the N. E., but towards 

 the S. W. There is therefore a total change of inclination 

 from north to south, or rather from N. W. to S. W. This 

 regularity in the mode of deviation, which often occupied 

 my attention in passing over the Andes, has lately engaged 

 the attention of M . Steininger (Erloschene Vulkane, p. 3). and 

 of M. Reboul, (Journ. de Physique, 1822, December, p, 425), 

 on the banks of the Rhine, and in the Pyrenees. 



VOL. VI. 2 R 



