500 0. H. HERSHEY GEOLOGICAL RECOKKAISSANCE IX NICARAGUA 



water stage of the river. The face of the bluff presents fine exposures 

 of the material. At the base is a dull olive gray, claylike material which 

 may be a decomposed volcanic tuff. Portions near the top are stained 

 to an intensely red color. The surface of the claylike member is undu- 

 lating. It is overlain by a bed of slightly cemented gravel, which ex- 

 tends to the top of the bank and may be 25 feet thick in places. The 

 pebbles are well water-worn and average between one-half and 1 inch in 

 diameter (rapid estimate), though some are 5 inches in length. Most 

 of them consist of hard white quartz, and not sufficient time was avail- 

 able to determine the other rock species represented. The gravel is 

 white in color, with a light red stain in the cementing material. The 

 entire deposit is roughly stratified, but I could not determine whether 

 it is marine or fluviatile in character. No shells were seen in it. 

 Springs of water come out at the base of the gravel, as the underlying 

 formation is relatively impervious to water. 



This bluff is the northward end of the so-called "Pine Eidge," which 

 is said to extend to the Wawa Eiver and to be represented both north of 

 the Wanks Eiver and south of the Wawa Eiver. It is described as a 

 broad rolling upland, in places a succession of small hills, with many 

 small creeks in the ravines. At Saclin the surface is distinctly but 

 smoothly rolling, suggesting that it is a remnant of an old dissected 

 plain, either a coastal plain or an old delta plain. The characteristic 

 feature of it is the growth of pine on it. It is said that away from the 

 vicinity of the streams there is no underbrush, but a great open pine 

 forest. The tree resembles the southern yellow pine of Louisiana. I 

 attribute its presence in a country which elsewhere abounds in the 

 tropical type of vegetation to the gravelly composition of the subsoil, 

 which makes the ''ridge" a region of relative aridity unfavorable to the 

 tropical vegetation. The "ridge" country is said to have a black soil 18 

 inches deep and below that a great bed of white gravel. 



The 35-foot bluff extends to at least a mile above Saclin. Much of 

 the gravel member is white in color and stands with a vertical face. 

 The claylike member under it resists erosion and, seen from a short dis- 

 tance, resembles hard rock. Then the river swings away from the bluff 

 out into the broad floodplain and is bordered by gravel bars or steep 

 banks of gravel and brown sand about 15 feet high. The river again 

 touches the 35-foot bluff on the south side about 10 miles above Saclin. 

 Bright colors appear, but the bank is largely covered by vegetation. 

 From the top a plain is said to extend to and connect with the "Pine 

 Eidge." Several miles farther upstream the south bank of the river 

 exposes a section similar to that at Saclin, except that the lowest stratum 



