the marsh, consis 
JENNINGS: FERNS OF THE ISLE OF PINES 131 
practically all around the northern portion of the island 
by a broad belt of the mangrove formation. There appears 
to have been in recent times an elevation of the island 
sufficient to have enabled the streams to cut down steep 
channels, at least in the lower part of their courses, so 
that subsequent depression to the present level has re- 
sulted in submerging the lower courses of the rivers, 
thus making them subject to tide water for often eight 
or nine miles from the mouth. The forests of the man-_ 
grove formation have at the same time advanced upon 
the lower parts of the depressed plain. : 
The soil of the greater part of the in and plain nae. 
of a yellowish red or brownish red gravelly clay, known 
as the Mal Pais Gravel. This soil is evidently residual, 
being derived by subaerial erosion from underlying 
marbles and schists. In depressions, and especially on 
the low plain below the contour of the ancient elevated . 
sea cliffs, the Mal Pais Gravel is replaced bya light yellow a 
or somewhat gray sandy loam. In the west eentral bes 
around Los Indios th there are 
_ pure glistening white quartz gravel and 0 coarse , sand S 2 
mixed here and there with more or less iron. Towards the 
coastal fringe the soil becomes: alluvial, being 20) mpos ea 
of varying mixtures of beach deposits and remains < - 
_ vegetation. oa 
The southern component of the itor et south 
- writer, of a rather 1 
but little elevate 
along the median 
_ where reached by t 
eat voy by the th oe 
