100 



OBSERVATIONS. 



Conformable transition rocks cover the primary, and sometimes 

 alternate with them ; they are also associated with the lowest beds of 

 the coal formation, so that no well marked division can be traced be- 

 tween them : but there is one character, independent of all artificial 

 arrangements, which serves to distinguish transition rocks from the 

 upper secondary strata, in countries where the regular coal formation 

 is found. All rocks under the coal formation, belong either to the 

 transition or primary class ; and all the strata above the coal forma- 

 tion belong either to the secondary or the tertiary class. The geo- 

 logical position of the regular coal formation thus serves as a simple 

 and intelligible key to the geology of all countries, wherever it occurs. 

 But where the coal strata are absent, the difficulty of determining the 

 class to which certain rock formations belong, is often very great. Of 

 this we have a striking instance in the perplexed attempts of foreign 

 geologists to classify the vast calcareous formations of the Jura, and 

 the outer range of the Alps ; and the perplexity is further increased, 

 by the mistakes which are made in referring to the English mountain 

 limestone, by confounding it with the calcaire alpin, or alpine lime- 

 stone. The alpine limestone, according to some geologists, is a trans- 

 ition limestone ; but according to other geologists it is analogous to 

 the magnesian limestone under the new red sandstone, and also com- 

 prises the lias limestones and the oolites. Indeed, I am convinced 

 that in the vicinity of the Alps, rocks analogous to the chalk forma- 

 tion have not unfrequently been classed with transition limestones. 

 These mistakes have arisen from a desire to make observations agree 

 with preconceived theories, and with the artificial arrangements which 

 Werner had invented. Thus it was taken for granted, that the gran- 

 itic mountains of the Alps being primary, the calcareous mountains 

 must be primary also ; and when organic remains were first discov- 

 ered in them, the geologists in France were greatly surprised, and 

 seemed unwilling to admit the fact : at length, by a painful and re- 

 luctant effort, they removed all these mountains from the primary to 

 the transition class. A more Herculean labor remains to be perform- 

 ed, — that of removing many of these mountains still higher, to the up- 

 per secondary class. In the vicinity of Moutiers, in the Tarentaise, 

 where M. Brochant first observed some organic remains supposed to 

 belong to transition rocks, I discovered the Patella and other fossils, 

 peculiar to the upper secondary strata. 



In parts of France at a distance from the Alps and the Jura, the 

 mineral character of the secondary strata might alone serve to identify 

 them with the English lias, oolites, and chalk ; but in the range of the 

 Jura and the outer ranges of the Alps, the calcareous formations are 

 of such immense magnitude, and the beds are often so highly indura- 

 ted and crystalline, that it is only from their relative position and im- 

 bedded fossils, that we can trace their analogy to the English strata, 

 or to the secondary strata in the north of France. 



