MUSEUM OF COMPARATIVE ZOOLOGY. 253 



of the horizons and the alteraations 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. Way laud 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 bluti's. 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 fii'st 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 



