268 BULLETIN OF THE 
The Soboruco, or Elevated Reef Level. — The general extent and topo- 
graphic character of the soboruco is explained on a previous page. It 
forms the lowest bench immediately adjacent to the entire north coast 
and along the Santiago front, and is topographically and geologically an 
elevated coral reef. Synchronous with this level are the elevated playa. 
deposits in the harbors, and the elevated cienaga or mud neg on the 
south side of the island at Batabano. 
The Beach and Clif Terraces. —On the east end of the er the north 
coast is marked by three distinct and abrupt cliffs and terraces cut out 
of the steep slope of the old six-hundred-foot plain, or the Cuchilla level, 
which forms the highland. Between Cape Maysi and Baracoa the coast 
is practically inaccessible. The three terraces seen in this region are so 
clear and distinct that they are readily visible at one view, and their 
continuity is clearly traceable for miles. They can be best understood 
from the accompanying figure (Plate I. Fig. 6), and a description of the 
coast adjacent to the mouth of the Yumuri of the east. Here the river 
empties directly into the sea through a precipitous cafion affording a 
fine cross-section of the benches, so that their architecture and origin 
can be seen. The coastal scarp consists of three narrow sub-level 
benches, each surmounted by a vertical cliff. Bench No. 1 is the first 
sub-level strip above the sea. This in general represents the level of 
the elevated reef, which nearly everywhere forms the low-lying coastal 
plain and breaks off at the sea in a surf wall some ten feet in length. 
Its interior margin against the base of the first great cliff is forty feet 
high, and it nowhere exceeds one hundred yards in width. Imme- - 
diately off the mouth of the Yumuri River, however, a gravel delta fan 
spreads out in brackish water, a hundred yards or so on each side. 
The present submerged fringe reef does not grow immediately where 
this delta fan is being deposited across the river mouth, but appears on 
each side. If the present bottom, constituted as above, should be ele- 
vated forty feet, it would produce a beach exactly similar to the elevated 
one now seen ; that is, it would be composed of alluvial gravel imme- 
diately where the river once emptied, and of coral limestone a hundred 
yards or more on each side of it. 
This lowest terrace (No. 1), which is usually formed of elevated reef 
rock, is composed of alluvial gravel immediately off the cut of the river, 
and of elevated reef rock a quarter of a mile away seaward. This lowest 
bench consists of several small levels, the uppermost of which is the 
specially well defined alluvial gravel plain. 
This old beach abuts against a cliff (No. 2) about one hundred and 
