132 



ox THE TOPOGRArilY AXD GEOLOGY 



Barrei'O, thence back of the Mogote, and doubles on itself, bending to almost all points 

 of the compass until, descending a comparatively short distance, it enters a muddy 

 little river-bottom, the caiion of the Jimenoa, south or southwest of Jarabacoa. 

 Almost as soon as the traveller leaves the town he finds himself passing over a hard 

 coarse-grained syenite, not unlike "Quincy gi-anite " in its general appeai'ance. It is 

 a part of the same eruption as the peak of the Yaqui, and forms also the Mogote 

 Mountain and a few of the ridges, but has dwindled here to a comparatively small 

 streak. South of it the slates reappear, but along the trail on the summit of the 

 ridge there are exceeding few exposures, and the slates being soft there are but few 

 pieces in the soil. It seems to be mostly of a semi-talcose character and usually of a 

 reddish color, though occasionally the familiar greenish-gray was observed. The 

 Jimenoa at the crossing had abundance of syenite pebbles and comparatively few of 

 the slate, the latter btiing much softer. After crossing the river the trail follows the 

 bottom a short distance and then climbs another ridge, but not so steep oi" ci'ooked 

 as the previous one. Following this summit, the whole being in pine forest except 

 in the depressions where other trees make their appearance, the trail crosses the Tireo, 

 the longest branch of the Yuna, here a little rivulet, and then crossing another low 

 divide," descends into a long flat valley clothed with grass. Just before ^'caching 

 the valley, there is a good exposure on the hill side of a dark red conglomerate, the 

 color of an over-bui'nt brick. This is the more striking since it is the only bed con- 

 taining pebbles along the whole route, the slates everywhere else being of very fine 

 grain. The valley of Constanza must be two or three miles long and is as flat as a 

 billiard table. It is without doubt the bed of a now dried-up mountain lake, that 

 emptied itself through the canon of the Limon Kiver. The greater portion of the 

 drainage entered it at the southern part, while the upper end Avas rather " back 

 water." As a consequence, the soil of the lower pai"t is more gravelly, while that of 

 the northern end is a finer sand and clay. The upper end is entirely grass-grown 

 except on the margin ; but towards the middle it is covered with scattered clumps 

 and tongues of pine timber, which clothe the entire southern portion. ISTear the 

 southern edge the Limon River flows across the vallc}^, cutting its Avay between 

 bluffs of coarse gravel twenty feet high, made up of pebbles of syenite and sandstone ; 

 some of the boulders are more than two feet across. The Cienega, near the head of 

 the Yaqiii, was another such lake at a comparatively recent period, and even yet it 

 has not drained itself completely. If the Yaqui River, which there I'uns to one side 

 of instead of through the marsh, Avere to lower its bed a foot or tAvo — if it Avere to be 

 deflected so as to run through it, or if a comparatively small channel should be 

 opened from the mai-sh to the I'iver — in a little Avhile it Avould empty itself of its 



