chap. xiii. Crystalline Rocks of, 433 



Near M. Video, the space which I more accurately 

 examined was about fifteen miles in an east and west 

 line, and here I found the foliation of the gneiss and the 

 cleavage of the slates generally well developed, and ex- 

 tending parallel to the alternating strata composed of the 

 gneiss, hornblendic and chloritic schists. These planes 

 of division all range within one point of east and west, 

 frequently east by south and west by north ; their dip 

 is generally almost vertical, and scarcely anywhere 

 under 45° : this fact, considering how slightly undula- 

 tory the surface of the country is, deserves attention. 

 Westward of M. Video, towards the Uruguay, wherever 

 the gneiss is exposed, the highly inclined folia are 

 seen striking in the same direction ; I must except one 

 spot where the strike was NW. by W. The little 

 Sierra de S. Juan, formed of gneiss and laminated 

 quartz, must also be excepted, for it ranges between 

 [N. to NE.] and [S. to SW.] and seems to belong to 

 the same system with the hills in the Maldonado 

 district. Finally, we have seen that, for many miles 

 northward of Maldonado and for twenty-five miles 

 westward of it, as far as the S. de las Animas, the folia- 

 tion, cleavage, so-called stratification and lines of hills, 

 all ranges NNE. and SSW., which is nearly coincident 

 with the adjoining coast of the Atlantic. Westward of 

 the S. de las Animas, as far as even the Uruguay, the 

 foliation, cleavage, and stratification (but not lines of 

 hills, for there are no defined ones) all range about E. 

 by S. and W. by N., which is nearly coincident with 

 the direction of the northern shore of the Plata : in the 

 confused country near Las Minas, where these two great 

 systems appear to intersect each other, the cleavage, 

 foliation, and stratification run in various directions, 

 but generally coincide with the line of each separate 

 hill. 



