INTRODUCTION 495 



rocks in the silver-mining district of Depilto in Segovia as consisting of 

 quartz and gneissoid beds which he likens to the fundamental gneiss of 

 Canada. They are soon succeeded, in going down the valley of the De- 

 pilto, by overlying, highly inclined and contorted schists, "with many 

 small veins of quartz running between the laminae of the rock." The 

 Depilto is one of the headwater tributaries of the Eio Wanks. 



He describes the rocks in the Santo Domingo district, which lies about 

 115 miles south of the Pis-Pis district, as "dolerytes, with bands and 

 protrusions of hard greenstones." The "doleryte" is decomposed to a 

 depth of at least 200 feet. He says : 



"This decomposition of tlie rocl^s near tlie surface prevails in many parts of 

 tropical America, and is principally, if not always, confined to the forest re- 

 gions. It has been ascribed, and probably with reason, to the percolation 

 through the rocks of rain-water charged with a little acid from the decom- 

 posing vegetation." 



Mr. Belt describes a ridge crossed by the road between San Rafael 

 and Ocotal as 



"very steep, and fully 1,200 feet high, composed entirely of boulder clay. This 

 clay was of a brown color, and full of angular and subangular blocks of stone 

 of all sizes up to 9 feet in diameter. . . . This boulder clay had extended 

 all the way from San Rafael, and ranges of hills appeared to be composed 

 entirely of it. The angular and subangular stones that it contained were an 

 irregular mixture of different varieties of trap, conglomerate and schistose 

 rocks. . . . The evidences of glacial action between Depilto and Ocotal 

 were, with one exception, as clear as in any Welsh or Highland valley. There 

 were the same rounded and smoothed rock surfaces, the same moraine-like ac- 

 cumulations of unstratified sand and gravel, the same transported boulders 

 that could be traced to their parent rocks several miles distant. . . . The 

 immense ridges of boulder clay between San Rafael and Yales. the long hog- 

 backed hills near Tablason, the great transported boulders two leagues beyond 

 Libertad on the Juigalpa road, and the scarcity of alluvial gold in the valleys 

 of Santo Domingo could all be easily explained on the supi)osition that the ice 

 of the Glacial period . . . covered all the higher ranges, and descended in 

 great glaciers to at least as low as the line of country now standing at 2,000 

 feet above the sea." 



J. Crawford, the government geologist of Nicaragua, divides^ the 

 country into five zones, the first or central zone made up of "Lauren- 

 tian, Taconic, Cambrian, and Silurian rocks in the form of granites, 

 gneisses, sandstones, porphyries, slates, quartzites, limestones, and horn- 

 blendes." The second division, a narrow beU on the east of the first, 

 contains Carboniferous limestones, Permian magnesian limestones, red 



' Abstract of a paper entitled "The Geology of Nicaragua." Proc. Amer. Asso. Adv. 

 Scl., vol. xl, 1891, pp. 261-270. 



