MUSEUM OF COMPARATIVE ZOCLOGY. 253 
of the horizons and the alternations-of lithologic material shown in the 
local sections, such as the great beds of fine siliceous and argillaceous 
mixtures with the lime, as noted at Matanzas and seen from there east 
to Baracoa, forming thick strata of yellow material, containing, at least 
at Baracoa, Miocene Mollusca and corals, as determined for me by Dr. 
Dall and Mr. T. Wayland Vaughan. (Plate I. Fig. 5. 3.) 
The slightly arenaceous yellow beds outcrop at Nuevitas, Gibara, and 
many other places along the coast, and are included between thicker strata 
of limestone, and I think they are underlain by several hundred feet of 
that material, and belong near the limestone capping Yunque and the 
Yumuri bluffs, These yellow bluffs underlie the soboruco reef at» Bara- 
coa, and are capped by a thick stratum of old limestone back of the city. 
The harbor is largely formed by their undermining. They are also well 
developed beneath the old reef points of Mata Bay. 
A peculiar rock material in the old limestone series at Baracoa, and not 
seen elsewhere, is a hill (Plate I. Fig. 5. 4) of almost vertically stratified 
siliceous material, which at first sight resembles gray chalk, but has the 
light specific gravity of some of the diatomaceous earths. Under the 
microscope this material is found to be composed largely of siliceous re- 
mains of minute organisms, mostly of Radiolaria, with sponge spicules and 
echinoid fragments, but containing no diatoms, so far as I have studied it. 
This material is distinctly stratified, and contains oocasional thin separa- 
tion layers of a gray-blue clay and some flint-like siliceous nodules. It has 
clearly undergone great disturbance, as is shown by the vertical arrange- 
ment of its beds, and apparently lies below the yellow beds, which are 
Miocene, as determined by Dr. W. H. Dall. This material has always 
been a source of great perplexity to the. people of Baracoa, who could not 
classify it or understand its qualities. The reservoir for the village 
water-works is located upon the single hill where it outcrops, on the 
southwest side of the harbor. The beds are over five hundred feet in 
thickness, and I think they overlie the oldest of the limestones, but this 
I could not ascertain with certainty. Neither this material nor the 
yellow beds which together constitute at least five hundred feet of the 
tertiary sequence can be classified as of coralline origin. 
The Post-Tertiary Folding.— The chief feature which separates the older 
limestones into a distinct system from the modern reef rock is the strati- 
graphic unconformity between them, and the fact that the former have 
undergone great folding and disturbance prior to the deposition of the 
latter, which are always subhorizontal. In no locality have I seen the 
newer reef rock folded or greatly pitched, but the older limestone is 
