OF SANTO DOMINGO. 



181 



the mountains as passing entirely over slates which also extend down the Gnananitos 

 Creek. The heavy river deposit in the J aina and its valley covers np whatever rocks 

 may exist at this part of its course ; but its head, which lies far to the northwest of 

 the mouth of the Guananitos, is up a steep, narrow, and exceedingly rough canon, and 

 entirely in syenite of constantly changing lithological characters. This is the broad 

 mass which is alike encountered on the Maimon Kiver east of Mount Yanilejo, on the 

 Majoma, the Upper Nigua, and even sends dykes across the l^izao almost to 

 Maniel. 



The exact point Avhere the pass enters the syenite on the river is not certain on 

 account of the river deposit above mentioned, and which consists of gravel and 

 boulders of intrusive rocks exclusively, l^eav los Matas Mr. Speare found two rocks, 

 the more peculiar because of the large amount of hornblende in most of the syenite 

 of the Jaina. They were not in place, although fragments of them were so abundant 

 as to imply that their source, most probably a dyke, was not far distant. One is a 

 soft yellow mica slate, the mica which makes the greater part of the mass being of a 

 light brownish-yellow color ; the other is a compound of white quartz and yellow 

 feldspar, in which I am unable, with the glass, to detect any other mineral. South- 

 west of this, five miles above Catare to the west of the road, and northwest of Mount 

 Basimo, he obtained a dark-colored actinolite slate. This is not far from the syenite. 

 In this same region a little gray limestone is found dipping northeast, and just north 

 of Mount Bassimo a brown earthy shale occurs seamed with calc spar. This moun- 

 tain, which is a western spur of the Mariana Chica ridge, is traversed by a heavy 

 dyke of syenite, some of which is made up of white quartz, white glassy feldspar, 

 and little black specks of hornblende, while other parts seem to approach a porphy- 

 ritic structni'c, consisting of large ciystals of glassy feldspar and large grains of 

 quartz imbedded in a matrix of a finer material of smaller quartz grains mixed with 

 minute specks of hornblende, A similar material was found on Upper l^igna, whei'c 

 the feldspar is of a flesh-color. It differs from a ti-ue porphyry in that the matrix is 

 resolvable even to the naked eye into its component minerals, and the included 

 crystals are both quartz and feldspar. The high range east of Bassimo which sepa- 

 rates the waters of the Jaina from those of the Ozama and its tributaries and which 

 give rise on its eastern side to the Isabella, is made up of clay slates rarely talcose 

 and sometimes jaspery. They are much traversed by quai'tz veins, some at least of 

 which are auriferous. A little gold has been found in the bed of the Isabella, though 

 not enough to be of importance. In the latter river a greenish-gray fissile claystone . 

 ■ s the prevailing rock. On tho summit of Mariana Chica the same rock is jnspei-y, 



A. P. S. — VOL. XY. 2t. 



