EXCURSION TO THE PYRENEES 33 



mines of Rancie were visited. The deposit here consists of a 

 large body of limonite of irregular shape, enclosed in Silurian 

 limestones and shales, and nearly coinciding with them in dip. 

 It is worked by a series of levels the lowest of which is at Sem. 

 This ore body which is very extensive has been mined for ages 

 and formerly supplied ore to as many as fifty Catalan forges, 

 which were in blast in the vicinity. The ore which is handled 

 in a rather primitive manner is now sent to Tarascon, where it is 

 smelted in the blast furnaces situated there. The limonite which 

 makes up the mass of the deposit that has been worked up 

 to the present time, is derived from the alteration of spathic iron 

 ore into what the ore body changes in depth. 



Taking a little path up the mountain beyond Sem, a summit 

 marked by the Croix de Ste. Tanoque was reached, where an 

 occurrence of lherzolite is well exposed. This is the original 

 locality of the "Lherzoline" or " Lhercoulite " of Cordier, who 

 mistook the somewhat altered and serpentenized rock for a dis- 

 tinct variety, to which he gave this name. The Jurassic lime- 

 stones are here penetrated and altered by the intrusion, being 

 bleached and crystallized, while the blocks of the light colored 

 dipyre hornstones found near the contact are considered by 

 Lacroix to be impure or marly bands which were interstratified 

 with the limestones and which by virtue of their peculiar com- 

 position were able to fix the exhalations from the lherzolite, 

 which the limestone was unable to do, and in this way to yield a 

 rock rich in dipyre, microline, orthoclase and a variety of other 

 silicates, the original differences in the composition of the beds 

 becoming accentuated through the action of selective metamor- 

 phism. 



Leaving Vicdessos the following morning, the party traversed 

 the forest of Freychinede, climbing up great exposures of the 

 Jurassic limestone, blue in color and often brecciated, the color 

 being bleached out in spots and streaks precisely as in the Jurassic 

 limestones of the Alps. In these limestones are several occur- 

 rences of lherzolite and ophite, which according to Lacroix 

 have the form of laccolites, and which alter the limestones 



