S18 M. Arago on Artesian Wells 



formations, all the phenomena exhibit themselves on a much 

 larger scale, on account of the prodigious thickness of the strata, 

 of their rarer alternation, and the greater velocity of the cur- 

 rents of the subterranean waters. This at once supplies an ex- 

 planation of the circumstance that the natural springs in the se- 

 condary formation are, at the same time, so rare, and yet so 

 abundant. 



We shall now I'eview, in detail, the consequences which we 

 have deduced from the individual forms and characters of these 

 two stratified formations, and shall notice how far observation 

 confirms the accuracy of our conclusions. 



Water Jhws freely, at all depths, in Chalk. 



For the proof of this I shall do nothing more than adduce 

 the instance of the many real jets d'eaux which proceed, at all 

 heights, from the fissures which indent the steep ascents of Cape 

 Blanc-Nez and Cape Gris-Nez, in the department of Pas-de- 

 Calais. There Nature may be seen in her secret operations. 



Among Strati/ted JRocks t/iere are great Chasms and Caverns. 



When we think of the great labour and art which mankind 

 employ, in erecting even small arches and vaults, for the sus- 

 taining of great weights, we are almost averse to allow that in 

 the subterranean regions there can be any thing like vast and 

 noble halls : a very slight examination, however, of a great num- 

 ber of examples, will very soon put us right on this point. 



The famous rock of Torghat, in Norway, is, as is well known, 

 pierced from end to end by a rectilinear opening 150 feet high, 

 and more than 3000 feet long. How insignificant in comparison 

 of this all the arches of man's formation ! 



The cavern of Guacharo, in the valley of Caripe in South 

 America, of which my illustrious friend M. Alexandre de 

 Humboldt has given us so interesting a description, has for its 

 vestibule a vault 72 feet high by eighty feet wide, appearing 

 near the summit of a vast rock of that peculiar species of 

 secondary limestone known under the name of Jura limestone. 

 This cavern maintains all the dimensions of its vestibule, and in 



