128 M. Charbaut on the 



I imagine the principal cause of this di£5culty was owing 

 to the perfect resemblance that frequently exists in the se- 

 condary class, between rocks situated at great geological 

 distances from each other, and consequently to the confusion 

 resulting from it, of many formations absolutely diiferent. 



Since the consideration of fossils in the distinctive cha- 

 racters of rocks has led Messrs. Cuvier and Brongniart to 

 the excellent results contained in their memoir on the mi- 

 neral geography of the environs of Paris, many geologists 

 have followed this new route; and there is no doubt that 

 from their steps being more certain, they will much sooner 

 be led to the end proposed in geology, which is to under- 

 stand the relative position of all the mineral masses of the 

 surface of the globe that man can reach. 



The Jura mountains, excessively rich in very various 

 fossils, is, perhaps, of all geological sites, the most proper to 

 be examined in this point of view ; the most undeniable 

 traces of dreadful convulsions, afford besides, at every step, 

 the image of disorder and chaos ; the fractures, the upset- 

 ting of beds, the subsidence of entire mountains, cause such 

 surprise, that, notwithstanding the best formed resolution of 

 only verifying facts, the observer is naturally led to ascend 

 to the first causes of all he sees, and cannot avoid deep and 

 prolonged meditation. 



M. Brongniart had visited in 1817 a considerable portion 

 of the Jura chain, in a geological point of view, and will 

 probably publish the result of his observations ; but as he 

 has not visited the environs of Lons-le-Saunier, I shall en- 

 deavour to make known the geological structure of that 

 country. 



In order to render this memoir more easily understood, 

 the following is the order I adopt : I commence by dis- 

 tinguishing the great formations ; I develope the composi- 

 tion of each of them, beginning with the lowest masses, 

 geologically speaking, and following them in the order of 

 height to those that crown the country, with which I occupy 

 myself; I shew their geographical disposition; and although 

 piy end is not to give the mineral geography, I yet notice 



