l>ftE)-VOLCANiC SEDiMENTARIES 515 



in gently inclined beds. The rock at the Little Falls below the Pis-Pis 

 bodega is dark red andesite lava. 



In descending the Tunkey Eiver from Barbones, at ll^ miles the val- 

 ley is constricted and passes through a range of hills of augite andesite, 

 as indicated by the sudden appearance in the stream-bed of many 

 boulders of hard, very dark greenish gray crystalline rock. About 4 

 miles in a straight line east-southeast of Barbones a rock appears that 

 seems to be a fine-grained quartz with disseminated pyrite, possibly an 

 altered sedimentary rock. However, farther down the river we found 

 many boulders of the hard greenish andesite. High hills near the river 

 and many sections abounding in these boulders indicate that even though 

 sedimentaries may be present there is much igneous rock all the way to 

 Tunkey. Back of the village there is much of the hard dark greenish 

 rock, and also a light yellowish green rock that may be an altered lime- 

 stone. 



Pre-volcanic Sedimentaries 



E. B. Stanford, the former manager of the Siempre Viva mine, says 

 that limestone appears about 3 miles south of the mine and spreads 

 thence southward over a broad country. At the La Luz mine shale is 

 associated with it. He says that from the apparent relation between the" 

 limestone and lava south of the Siempre Viva mine the limestone surface 

 may appear 1,500 to 1,800 feet below the surface at the mine. A piece 

 of the limestone which Mr. Stanford gave me was among the specimens 

 submitted to Doctor Lawson and was described as follows : 



XI. The rock is a compact, dark-colored, fine-grained limestone, composed 

 chiefly of large calcitic areas and a fine-grained part, which is seen to be made 

 up of organic tests. Pyrite occurs in scattered cubes throughout the section. 



My impression is that the northern border of the old sedimentary ter- 

 ranes trends easterly or southeasterly from the point 3 miles south of 

 the Siempre Viva mine, and that all of ISTicaragua north of it and west 

 of the old coastal plain may be occupied by the igneous rocks described 

 in this paper. Crawford vaguely refers to a disconnected line of lime- 

 stone areas between the "granite" hills and the Wanks Eiver, but I saw 

 no evidence of them in the gravels of streams draining from that area, 

 and at best they must be very limited in size. Andesitic lavas and tuffs 

 are certainly the prevailing rocks in a great area. In the mountain re- 

 gions they have been extensively intruded by other andesites and some 

 rhyolites. Belt's "dolerytes, with bands and protrusions of hard green- 



