OF SANTO 1)OMTN(IO. 



83 



PART II. 



GEOLOGICAL FORMATIONS. 



CHAPTER IV. 



THESIERRAGROUP. 



ISTo formation older than the secondary era, has been found on the Island ; the 

 oldest group, being the great mass of slates, conglomerates and limestones which 

 form its core. These are uptilted and broken by numerous intrusive masses of crys- 

 talline rocks which may be, for convenience, grouped under the generic term of syenite, 

 since they almost invariably consist of the three necessary minerals, quartz, feldspar, 

 and ho]"nblende. 



Flanking the slates, etc., of the Sierra, there is a broad development of Tertiary 

 marking all the northern and a part of the southern side of the Island, and this in turn 

 is bordered by a more recent deposit of limestones and gravels which I shall call the 

 coast formation. 



The Sierra group forms all of the gi'eat mountain mass of the interior, extending 

 the entire length of the Eepublic* 



It also constitutes the greater part of the Peninsula of Samana, and appears as a 

 single little outlier, under the Tertiary, near Puerto Plata. It everywhere shows the 

 evidence of active subterranean forces, being not only metamorphosed, with hardly a 

 single local exception, but is everywhere much uptilted, and usually, strongly folded. 

 Over much of its area, the metamorphic action has been so complete as to destroy the 

 traces of stratification, or to so nearly obliterate them, that they are apt to be con- 

 founded with cross fractures. This is most markedly the case in those regions, 

 esj)ecially in the eastern half of the Island, where the rocks take on a serpentinoid 

 character. I^ear Yamasa, for instance, I amused myself on the face of a fine bluff in 

 trying to decipher the lines, and found that I could construe them to suit any theory 

 of direction of dip desired. The same thing occurs again at Piedra Blanca on the 

 Maimon Eiver in the Province of Yega. 



But enough of the stratification is preserved to show conclusively that these beds 



* And it seems to form at least one, if not botli the long peninsulas of Hayti ; at least the appearance of the 

 moxmtains is such that it induced me to draw this inference when, a year or two ago, I skirted along the coast, a mile 

 or two off shore. The contour and general character of the mountain ranges of Hayti are identical with those of the 

 central range of Santo Domingo, — liigli, rough, irregular and heavily wooded. 



