310 C. W. HAYES — GEOLOGY OF NICARAGUA CANAL ROUTE 



most abundantly, however, near the Pacific coast, and are well exposed 

 in the headland northwest of the Rio Grande valley at J^rito. The beds 

 here have a general, though somewhat variable, dip to the southwest; 

 hence the higher portions of the formation make tbe cliffs along tbe 

 Pacific. This seems also to be its most variable portion. 



In addition to the shales which constitute its greatest Ijulk to the east- 

 ward, it here contains also beds of sandstone, conglomerate, and coarse 

 volcanic breccia on the one hand, and on the other marly beds and 

 lenses of pure limestone. Forming a part of the headland south of 

 Brito is a bed of limestone something over 100 feet in thickness. Small 

 outcrops of this bed, or one very similar, have been noted at several other 

 localities to the eastward in the divide hills. Its limited extent is due 

 in part to erosion, since the dip of the bed would carry it above the tops 

 of most of the hills to the eastward, but it is doubtful if its original ex- 

 tension was very great. Several of the limestone outcrops noted are 

 probabl}'' small lenses in the shale and not connected with the more 

 continuous bed at Brito. A portion of this limestone has a peculiar 

 concretionary structure, some of the concretions attaining a diameter of 

 an inch and a half while other portions of the bed are oolitic. 



Immediately west of this exposure of limestone, forming a group of 

 islets nearly covered by high tide, is a very coarse volcanic conglomerate 

 or breccia. The larger fragments are a foot or more in diameter and 

 quite angular, and from this extreme the}'' grade downward to small 

 pebbles, some of which are well rounded. The present relations indi- 

 cate that the conglomerate is the stratigraphical equivalent of the lime- 

 stone, replacing it within a few yards. In some places the two rocks are 

 seen to merge, the limestone containing numerous angular fragments of 

 volcanic rock. At other points along the coast both north and soutli of 

 Brito similar conglomerates occur. Their bedding is extremel}^ irreg- 

 ular, and they afford evidence of having been formed rapidl}^ and near 

 the source from which their constituents Avere derived. While it is pos- 

 sible that the source of this material may have been to the eastward, it 

 seems much more likely that it came from volcanic vents to the south- 

 west — from volcanoes which have been entirel}' removed by the waves 

 of the Pacific. 



Although their connection has not been continuously traced, it is as- 

 sumed that the sedimentary rocks found at various points along the 

 southern margin of the lake east of Sapoa belong to the Brito formatioui 

 This region was examined by coasting along the lake shore, so that it 

 was chiefly the rocks forming the projecting headlands wdiich were ob- 

 served. These consist almost entirely of sandstones ver}' similar in ap- 

 pearance to the sandstones found interbedded with the Brito shales, and 



