MODE III. LIMESTONE. 445 



flint are found in chalk, so layers of chert, or ke- 

 ralite, appear in limestone ; while Lydian stone, 

 and siliceous schistus, sometimes intersect the 

 primitive calcareous rock. 



Limestone often presents mural precipices, as 

 in the Pyrenees, and sometimes in forms ap- 

 proaching the artificial, as in the circus, towers, 

 and cylinder of Marbois. The picturesque ap- 

 pearances of Chedder cliffs are on a smaller 

 scale. In the chain of Jura, and in the Py- 

 renees, calcareous mountains have been ob- 

 served, with exterior arrects of 40 or 45 degrees, 

 while the interior become more and more verti- 

 cal. Palassou and Pasumot, in their descrip- 

 tions of the Pyrenees, have observed a mountain 

 of limestone, formed of oval and circular concen- 

 tric layers, which present a most singular ap- 

 pearance. On a smaller scale, as in pisolites 

 and sinapites, limestone often affects the orbi- 

 cular form. 



Saussure informs us, 347, that the chain of 

 Jura is calcareous, with the exception of some 

 few spots, covered with calcareous sandstone. 

 In 1937 he remarks contorted beds of compact 

 limestone, which he says of course must be sedi- 

 mental, not crystallised, and must have been 

 deranged by a refoulement* Nor has the re- 



