506 O. H. HERSHEY GEOLOGICAL RECONNAISSAlS^CE IN NICARAGtTA 



Hocks low in the banks, seen occasionally from the boat, appeared igne- 

 ous. Some limonite-cemented Modern gravel occurs under the brown 

 sand. At a gravel bar near the landing of the Santa Rita mine it was 

 difficult to distinguish any rock species except a few andesite pebbles. 

 The gravel is largely light-colored material, probably produced by the- 

 alteration of sedimentary rocks. There may be some chert from a lime- 

 stone area, some quartzite and some rock that resembles a decomposed 

 granite, but there is nothing definite about them. I suspect that the 

 region is largely one of sedimentary rocks abounding in intrusives. 



Thence the river is generally winding about in a broad floodplain, 

 though it occasionally touches the side of the valley and exposes rock and 

 low hills. The Wasaki Falls is caused by an outcrop of apparently 

 igneous rock. The same is true of the Walpitara Falls, though none was 

 secured for close examination. Below the falls the stream resumes its 

 interminable winding in the floodplain. Presently we passed a low bank 

 of dark red stratified material tilted at an angle of about 70 degrees. 

 The coarser layers were speckled and had the appearance of an andesite 

 tufl. In a few hours evidences of bedrock had disappeared and we had 

 entered a region of deep water, winding constantly between 20 to 25 foot 

 banks of brown sand and silt. I^ext morning we passed a series of rapids 

 caused by reefs of rock of a nearly white to light gray color. Its general 

 appearance suggested a horizontally stratified fine-grained sandstone. 

 There were no hills near the river. The alluvial banks gradually became 

 lower, and gravel and even sand beds disappeared from them, being re- 

 placed by stratified brovv^n silt and massive, light-colored mottled clay. 

 A number of small rapids passed early next morning I suspect were due 

 to Modern alluvium locally cemented by limonite. We had entered the 

 delta country and could see no hills from the bank. Near the mouth the 

 river is deep and sluggish, 100 to 125 feet wide; the banks, of brown 

 silt, are about 8 feet high, and apparently back of the fringe of bamboos, 

 scattered trees and bushes on the river bank there is an open country, 

 either savanna or swamp. 



The 30 miles of the Prinzapulca River traversed is 100 to 150 yards 

 wide and winds about somewhat in the apparently swampy delta. The 

 town of Prinzapulca is situated on the south bank of the river between 

 the beach and the swamps. The Prinzapulca lias not built a prominent 

 headland into the sea as has the Wanks. The beach deposits average 

 several hundred yards wide and in general rise only a few feet above 

 ordinary high-tide level. They consist of brown sand with patches rich in 

 heavy black sand, presumably magnetite. There are a few scattered small 

 pebbles, and fine gravel is said to appear on the beach 6 miles south. 



