190 



ON THE TOPOGRAPHY ANY) CEOLO&Y 



whence a practicable outlet can be obtained from the canon towards Santo Domingo, 

 and that over a high hill, Loma Cristina, fifteen miles from the city. This, which is 

 the shortest route to an available shipping point, would necessitate twenty-one miles 

 of land-carriage at least ; or, in case of the very impi'obable contingency of a railroad 

 being built to San Cristobal, the ore wonld have to be carried nine miles on horse 

 or mnle-back before it could i*each the nearest point of the road. 



At the mine the country rock, which is a semi-jasper, strikes l^T. 30° W. Avith a 

 northeast dip of 54° nearly conformable with the position of the limestone further up 

 the river ; but ver}^ soon there is an anticlinal, and the strata towards Tablasas dips 

 to the southward. The jaspers are various shades of dark green and brown, and 

 wherever not too much fissured break with broad conchoidal fractures, but with 

 earthy, never perfectly smooth surfaces. In some parts they present peculiar appear- 

 ances, resembling porphyry. One green specimen before me is mottled Avith minute 

 black shining specks ; others shoAV similar marks, but gray, yellow or white in color. 

 These are certainly altered sedimentary rocks, although hand specimens might be 

 mistaken for eruptive in origin. Except in these colored grains they differ in no 

 respect from the other jaspers. It seems that a similar charactei' is exhibited by some 

 of the metamorphic rocks of Jamaica. The geologists found that near the dykes 

 some of the beds were " converted into semi-crystalline masses resembling porphyry 

 and sometimes trachyte." These changes are also accompanied by an incipient 

 development of crystalline minerals."* I found one loose piece of gray jaspery slato 

 in the bed of the I^igua, of which nearly a fourth of the surface was made up of flesh- 

 colored grains, apparently feldspar crystals, averaging over an eighth of an inch 

 across. Barrett describes from the southeastern part of Jamaica "porphyries and 

 hornblende rocks interbedded " with cretaceous strata, and compares them with Dar- 

 win's account of localities in the. Andes, "where poi'phyries which had flowed as 

 submarine lavas alternate with conglomerates composed of the same rocks, and are 

 overlaid with beds containing cretaceous fossils. "f 'No such condition of aflairs exists 

 in Santo Domingo. . . . . . , . . ; 



At Tablasas the limestone is again encountered striking east and west and dipping 

 on its southern margin south 25°. At its base it is divided into recognizable beds, 

 from which I obtained the measurement ; further south it becomes so massi^^e that 

 no stratiflcation can be detected either in the bed of the river or on the hill sides. 

 For several hundred yards it makes the bed and banks of the river in great masses 

 their bases, usually so surrounded with sand that it is not possible to detci mine 



* Jamaica Geological Report., p. 27. . " , 



' f Quart. .Tdiuh. Qcol. Soc, vol. xvi. p. 324. 



