154 



SCIENCE. 



[N. S. Vol. VIII. No. 188. 



up to the so-called Dakota sandstone that 

 caps the blufif at that point. The marine 

 Baptanodon beds here show a thickness of 

 thirty-five feet. Above these is a series of 

 fresh-water sandstones and shales, sixty- 

 six feet in thickness, which in places con- 

 tain remains of Laosaurus, a typical Juras- 

 sic Dinosaur. Immediately above these the 

 Cycads occur in a narrow layer of white 

 sandstone, and with them are various frag- 

 ments of bones. Next above are fifty-five 

 feet of strata containing vertebrate fossils, 

 apparently indicating the Atlantosaurus 

 beds. Above these are thirty feet of barren 

 clays, and over all is the sandstone regarded 

 as Dakota. 



Mr. Eeed has also sent me specimens of 

 the Cycads found at this locality. As he 

 has had an experience of twenty years or 

 more on the Jurassic of the West, and is 

 otherwise admirably qualified to ju^dge of 

 such horizons, his opinion is entitled to 

 great weight and should settle the ques- 

 tion for this locality. 



Mr. H. F. Wells, who has carefully ex- 

 plored the Black Hills Cycad horizon, and 

 sent to the Yale Museum over one hundred 

 specimens of these fossils, has also, at my 

 request, sent me a section, made near Black- 

 hawk, on the eastern rim of the hills, a 

 region which I have mj'self examined, al- 

 though not recently. This section indi- 

 cates that the Cycad horizon there is also in 

 the Jurassic, and not the Dakota, and this 

 is borne out by other localities in the same 

 vicinity. 



Professor L. F. Ward has published sec- 

 tions examined by him on the southwestern 

 border of the Black Hills in 1893. He 

 found no Cycads actually in place, but de- 

 cided that the horizon in which they occur 

 is Cretaceous.* I have recently placed in 

 his hands for description all the Western 

 Cycads in the Yale Museum. Our views, 

 however, do not at present coincide as to the 

 * Journal of Geology, Vol. II., p. 250, 1894. 



age of the strata containing them, but the 

 new facts which are now being brought to 

 light will, I trust, soon place this matter 

 beyond reasonable doubt. 



0. C. Maesh. 



Yale University, 

 New Haven, Conn., July 18, 1898. 



NOTES ON THE GEOLOGY OF JAMAICA. 



The eastern portion of the island of Ja- 

 maica, in the West Indies, is remarkable 

 for its high abrupt mountains, whose ragged 

 outlines resemble those of the high sierras 

 (not the volcanic ranges) of the Pacific 

 side of Central America and Mexico. These 

 mountains rise steeply from the ocean east 

 of Kingston on the south side and near 

 Port Antonio on the north side of the 

 island, and in Blue Mountain peak attain 

 an altitude of about 7,000 feet. The to- 

 pography is essentially that of subaerial 

 ei'osion, the sharp rocky mountain ridges 

 being due to the excavation of deep narrow 

 stream valleys in a great uplift which orig- 

 inally extended beyond the limits of the 

 island. 



So far as I have been able to learn from 

 observation and conversation with resi- 

 dents, the entire mass of this Blue Moun- 

 tain system, in the eastern end of the island, 

 is composed of one great white limestone 

 formation. This may be soft and chalky ; 

 it may be brecciated and in places quasi- 

 conglomeratic ; it may be a hard compact 

 fine-grained sub-crystalline white limestone 

 nearly free from fossils, as in the case of the 

 material used for macadam in the streets of 

 Kingston ; or the same white limestone 

 abundantlj' fossiliferous, as at Port Antonio. 

 This latter locality is an interesting one. 

 Eeef-building coral species are numerously 

 represented in the mass of the rock, and the 

 white formation is evidently a coralline 

 limestone. There are the casts of many 

 other marine species of shell-bearing ani- 

 mals, particularly gasteropods and allied 



