270 



SCIENCE. 



[Vol. XXII. No. 563 



thenyte, or augyte, or trachyte rocks, that aj^pear thickly 

 sprinkled with pyrites and magnetic and titanic iron ores; 

 these boulders were weathered toward their centres from 

 one to three inches, and were found to be auriferous — in 

 some instances, highly so; they differ in composition and 

 color from the hornblende and orthoclase granite mass 

 forming the axis and serrated ridges of the hills, also from 

 the boulders mixed with the patches of clay, sands, gravels, 

 and boulders that are found to the southward on these 

 granite hills and ridges. This filling up of former exist- 

 ing valleys with the materials worn off, in part, from the 

 granite ridges, evidences a subsidence in that locality at 

 the time, and this evidence is supported by the existence, 

 to the north of the granite hills and between them and 

 the Wauque, or Coco, River, of a disconnected line of 

 limestone; on one depression of this limestone a deposit 

 of the auriferous clays, sands, gravels, and boulders was 

 found. The eroding into hills and valleys, as they at 

 present appear, composed of the mass of detritus of disin- 

 tegrated granites, etc., is evidence of a subsequent eleva- 

 tion of that entire region and the completing of one oscil- 

 lation of subsidence and of re-elevation there. 



The moutonned ridges extend for about sixty miles in 

 a series of parallel oblong ridges northeastwardly from 

 near the base of the tall Barbar and Peiia Blanca Moun- 

 tains, that at present have an altitude of over 7,000 feet 

 above the Caribbean Sea. One of the p)rojecting lines of 

 moraines extends further northward, and is about ninety 

 miles long until it terminates at a dyke, on whose sides 

 auriferous gravels are found, in which the Rio Wauque 

 has cut its channel at San Ramon. 



This system of moutonned ridges extends to a width 

 eastward and westward of about twenty-five miles, and 

 has at present an altitude above the creeks at its base 

 of from 70 to 400 feet. They were found to be composed 

 most generally of unstratitled clays, sands, gravels, and 

 boulders ; occasionally, however, these materials are partly 

 stratified and partly assorted. The enclosed boulders 

 are of various sizes, from ten pounds to several tons 

 weight, and are usually angular or sub-angular, becoming 

 oblong and oval as the series of moutonned ridges extend 

 northward, i. e., towards the Wauque River, and are com- 

 posed most generally of fragments of auriferous quartz, 

 granites, syenites, hornblendic feldspatic rocks. 



These moutonned ridges have been denuded and eroded 

 by the very energetic and potent meteorological forces in 

 this locality, until numerous large boulders have been 

 displaced and lie on the sides and at the base of the 

 ridges; also numerous gulleys score deeply the sides of 

 these ridges, and deep ravines or channels of the flowing 

 creeks separs te many of them from each other. These 

 moutonned ridges are unquestionable evidences of a 

 glacial epoch and of a long-continued glacial flow at this 

 low parallel — only 14° north from the equator3 — which 

 covered quite a large part of the present existing narrow 

 divide of land (containing about 48,000 square miles) 

 between the Pacific Ocean and the Caribbean Sea. Ad- 

 joining the granite hills on the northward and north west- 

 ward,often between the moutonned and the granite ridges, 

 are a number of erosion-sculptured hills that have been 

 carved out by the draining forces attending the elevation 

 of lands in that locality, and evidence that elevation, and 

 subsequently by meteoric forces. These hills of erosion 

 are composed of the detritus of rocks transported by 

 water from the southeastern ending of the Matagalpa 

 system of mountains (a distance of seventy to eighty miles 



''At latitude 12^ 20' north from the equator similar moutonned ridges and 

 glacial epoch moraines were discovered on the south side of the southeastern 

 termination of the Matagalpa system of mountain ranges, and were examined 

 by the author of this paper in 1890, and reported on to the British Association 

 for the Advancement or Science, the American Association for the Advance- 

 meat of Science, and officially to the Government of Nicaragua. 



southwest), and of materials eroded from the adjoining 

 and nearby series of granite hills; the materials com- 

 posing them have been cemented and concreted into semi- 

 hard rocks and conglomerate masses of clastic rocks. The 

 altitude above the Caribbean Sea of many of these granite 

 ridges, erosion-formed Gerros and moutonned ridges, is 

 from 1,000 to 3,500 feet; all are covered with a dense 

 growth of large trees, or, in some places on the erosion- 

 formed ridges, covered with a jungle of trees, bamboos, 

 vines, and other vegetation. 



The reefs, or lodes, strike east of north and west of 

 south, parallel to the long axi.s of the ridges and moun- 

 tains, and those discovered usually dip at an angle of 

 about 120" south. They are from 6 to 30 inches wide, 

 and usually appear to be rich in gold and in metallic 

 suljjhides and arsenides. The reefs at the granite ridges 

 are parallel with those ridges, and found at the contact 

 between the granite and superimjoosed rocks (though 

 some appear to be in the granite) as principal lodes, from 

 which extend at various angles into the adjacent erosion- 

 carved Cerros many fissures containing the oxide of 

 metals, gold, sulphides, etc. Some few of these fissures 

 appear to continue northwardly into the moutonned 

 ridges; but this was not verified, because of the deep soil 

 and dense undergrowth that covers the surface of the hills 

 and valleys at that locality. The reefs parallel with the 

 granite ridges extend southwestwardly to near the Barbar 

 Mountains, where they appear to form an obtuse angle 

 with the auriferous reefs, or lodes, that extend (southeast 

 and northwest across Nicaragua) along the foothills of the 

 Matagalpa system of mountains, from the Caribbean Sea 

 to the Pacific Ocean. In the granite hills were discovered 

 two large deposits of iron ores, limonite and hematite, and 

 one dep)osit of manganese ore, the black di-oxide pyro- 

 lusite; also graijhite and some tin sulphide, stannite, 

 whether in paying quantities or not, i. e., profitable to 

 mining, has not been determined satisfactorily, because 

 they were found but recently, this year, 1893, in an unin- 

 habited wilderness; they are, however, in a thoroughly 

 mineralized locality. The auriferous reefs are of the 

 Dioritic gold-evolved era (as classified hj David Forbes, 

 P. R. S., in his paper "On the Geological Epoch at Which 

 Gold Has Made Its Appearance in the Crust of the 

 earth"),' and appear at the surface often where many 

 greenstone rocks were discovered. 



The auriferous placer deposits or leads of clays, gravels, 

 sands, gold, and boulders are of different geological epochs, 

 viz. : the strata of partly-cemented auriferous drifts of sands, 

 gravels, etc., exposed in patches, small to several acres, at 

 the sides near the base of the erosion-formed hills and 

 appearing to pass through those hills, and also found in 

 the upper valleys at varying depths beneath the surface 

 and at many places exposed in the banks along the sides 

 of the creeks. These leads of gravel drifts are from 8 to 

 20 inches thick, and although few masses of gold visible 

 to the unaided eye were observed in them, yet when they 

 had been washed out from a pan there were frequently 

 left in the pan jDarticles, grains, and small nodules of gold, 

 or occasionally laminated small masses of gold of angular, 

 sub-angular, and oval forms. These are "alluvial drifts," 

 or gravel beds, formed during the latter part, I am in- 

 clined to believe, of the Champlain epoch, and usually 

 contain only a small per cent of sub-angular and partly 

 rounded quartz. The gold found in them is in rather 

 coarse grains and particles, as described, and evidently 

 derived from three sources: 



(a) The auriferous reefs that traverse that part of the 

 country, and — 



(b) From the deeply disintegrated granite masses, and — 



(c) From the disrupted masses of quartz, pyrites, etc., 



*See London Geological Magazine, III., p, 385—7. 



