chap. xiv. Gypseous Formation. 487 



[B] of andesite whilst still fluid, and that owing to the 

 softness of the gypseous strata they have not acquired 

 the ordinary forms of dikes. Subsequently to the 

 injection of these feldspathic rocks, a great dislocation 

 has taken place ; and the much shattered gypseous 

 strata here overlie a hillock [G], composed of vertical 

 strata of impure limestone and of black highly calcare- 

 ous shale including threads of gypsum : these rocks, as 

 we shall presently see, belong to the upper parts of the 

 gypseous series, and hence must here have been thrown 

 down by a vast fault. 



Proceeding up the valley-basin of the Yeso, and 

 taking our section sometimes on one hand and some- 

 times on the other, we come to a great hill of stratified 

 porphyritic conglomerate [H] dipping at 45° to the 

 west ; and a few hundred yards farther on,, we have a 

 bed between 300 or 400 feet thick of gypsum [I] dip- 

 ping eastward at a very high angle : here then we have 

 a fault and anticlinal axis. On the opposite side of 

 the valley, a vertical mass of red conglomerate, con- 

 formably underlying the gypsum, appears gradually to 

 lose its stratification and passes into a mountain of 

 porphyry. The gypsum [I] is covered by a bed [K], 

 at least 1,000 feet in thickness, of a purplish-red, 

 compact, heavy, fine-grained sandstone or mudstone, 

 which fuses easily into a white enamel, and is seen 

 under a lens to contain triturated crystals. This is 

 succeeded by a bed [L], 1,000 feet thick (I believe I 

 understate the thickness) of gypsum, exactly like the 

 beds before described ; and this again is capped by 

 another great bed [M] of purplish-red sandstone. All 

 these strata dip eastward; but the inclination becomes 

 less and less, as we leave the first and almost vertical 

 bed [I] of gypsum. 



Leaving the basin-plain of Yeso, the road rapidly 



