OF SANTO DOMINGO. 



91 



epochs of the Cretaceous, while the newest are even more modern than the Miocene, 

 they are similar in composition and in all their leading features to what have hereto- 

 fore been considered peculiar to older geological periods. Richthofen'" dwells at 

 length on the idea that granites and "granitic rocks," as well as "porphyritic rocks" 

 are almost exclusively palaeozoic, quoting as a modern instance of the latter, the 

 Liassic age of some outflows in the Sierra ]S^evada of California, f 



The same author uses the fact of the eruption taking place during or subsequent 

 to the Tertiary as one of the characteristics in his description of "Volcanic rocks," 

 from which he strictly excludes all forms similar to those found in Santo Domingo. 

 The oldest eruptions here must have taken place after the deposition of the Cretaceous ; 

 but since we are not yet able to decide the exact jjosition in the scale for our Cretaceous 

 strata we are equally unable to determine the earliest possible epoch at which such 

 eruptions could have taken place. It could not have been earlier than the period of 

 the White Chalk of Europe (Senonien); and the probabilities are in favor of their 

 occurrence during the long Eocene period. Ample proof exists that the main range 

 acquired its present contour and nearly its present height, that the eruptive rocks had 

 appeared, and that the metamorphism of the Cretaceous was completed before the 

 deposition of the Miocene began. But another point yet remains not less remarkable 

 than the first, when examined in view of this theory. The Monte Cristi I'ange is 

 composed, with one or two insignificant local exceptions, of Miocene Tertiary. Its 

 elevation could hardly have taken place before the Pliocene, and possibly was not 

 completed until late in that era. ISTear the summit of the range, for a distance east 

 and west of forty or fifty miles, d3dves are not rare, and some of them are of con- 

 siderable size. These dykes are composed of a rock not only having a general resem- 

 blance to that of the Cibao range, but I have collected hand specimens north of 

 Macoris which would defy the most practiced eye to distinguish them fi'om portions 

 of the main central mass. ISTot only do they contain the same minerals, but those 

 minerals are combined in the same manner and proportion, and the general ajjpearance 

 of the two are the same. Yet it must be borne in mind that the Cibao rocks cannot 

 be later than the Eocene, while those in the Monte Cristi range cannot be older than 

 the Pliocene. The whole Miocene period intervened between the two sets of eruptions, 

 and still a uniformity of character was retained. IsTor can the objection be raised 

 that the resemblance is only a partial one, due to a second eruption in the Cibao 

 range synchronous with the dykes further north. It is not impossible that such was 

 the case, although I have never seen any reason to suppose so ; but granting it, all of 



* Loc. cit. pp. 9, 35, &c. 

 t Loc. cit. p. 41. 



