VARIETIES OF ROCK. 81 



The grunsteins of Tucutunemo, which we consider aa 

 constituting the same formation as the serpentine rock, 

 contain veins of malachite and copper-pyrites. These same 

 metalliferous combinations are found also in Franconia, in 

 the grimsteins of the mountains of Steben and Lichtenberg. 

 With respect to the green slates of Malpaso, which have all 

 the characters of transition-slates, they are identical with 

 those which M. von Buch has so well described, near 

 Schonau, in Silesia. They contain beds of griinstein, like 

 the slates of the mountains of Steben just mentioned.* 

 The black limestone of the Morros de San Juan is also 

 a transition-limestone. It forms perhaps a subordinate 

 stratum in the slates of Malpaso. This situation would be 

 analogous to what is observed in several parts of Switzer- 

 land, f The slaty zone, the centre of which is the ra>dne of 

 Piedras Azules, appears divided into two formations. On 

 some points we think we observe one passing into the other. 



The griinsteins, which begin again to the south of these 

 elates, appear to me to differ little from those found north 

 of the ravine of Piedras Azules. I did not see there any 

 pyroxene ; but on the very spot I recognized a number of 

 crystals in the amygdaloid, which appears so strongly linked 

 to the griinstein that they alternate several times. 



The geologist may consider his task as fulfilled when he 

 has traced with accuracy the positions of the diverse strata ; 

 and has pointed out the analogies traceable between these 

 positions and what has been observed in other countries. 

 But how can he Avoid being tempted to go back to the origin 

 of so many different substances, and to inquire how far the 

 dominion of fire has extended in the mountains that bound 

 the great basin of the steppes ? In researches on the posi- 

 tion of rocks we have generally to complain of not suffi- 

 ciently perceiving the connection between the masses, which 

 we believe to be superimposed on one another. Here the 



* On advancing into the adit for draining the Friedrich-Wilhelmstollen 

 mine, which I caused to be begun in 1794, near Steben, and which is yet 

 only 340 toises long, there have successively been found, in the transition- 

 ilate subordinate strata of pure and porphyritic grtinstein, strata, of 

 Lydian stone and ampelite (alanuschiefer), and strata of fine-grained 

 griinstein. All these strata characterise the transition-slates. 



t For instance, at the Glyshorn, at the Col de Balm, &c. 



fOL. il O 



