LAND SUBMERGENCE IN THE PLIOCENE. 125 



Matanzas depression, Cuba and the West Indies were reduced to small 

 islands without surface enough to furnish the red residual loams and 

 quartz gravel, such as make up the Lafayette of the northern continent. 



The Matanzas formation is widespread throughout the Antilles. In 

 San Domingo Gabb* describes this low lying formation as post-Pliocene, 

 on account of the modern aspect of the fossils, and calls it the " coast 

 formation," a name somewhat confusing, as it is also given to the modern 

 coral reef formations. Its thickness is about 200 feet. 



In Jamaica Sawkins'^ and other geologists describe the "white lime- 

 stone" as Miocene, but by some circumstance have tabulated the forma- 

 tion as post-Pliocene. It is a very much disturbed formation 2,000 feet 

 thick anil elevated to 8,000 feet above tide, altogether unlike tlie later 

 deposit in the Antilles. This has led to errors in correlations. In his 

 sunimar3\Sawkins describes the surface of the " white limestones " as a 

 " white marl " derived from the limestones ; but in the excellent detailed 

 local descriptions in numerous places he shows that the " white marls " 

 rest unconformably upon the " white limestones '' or older surfaces, the 

 marls having a thickness of not more than 200 feet. In Cuba, where un- 

 conformity or other criteria are not apparent, it is somcAvhat difiicult to 

 distinguish the Matanzas limestone from the older Tertiary rocks from 

 which it is largely derived. From the descriptions and also the map of 

 Mr Sawkins, it is apparent that the older Pliocene surfaces were enor- 

 mously eroded before the de])osition of the marls, as the latter lie in val- 

 leys hundreds of feet deep and three or five miles wide. The fossils 

 found are not abundant, but mosth^ belong to living species. 



A similar so-called post-Pliocene formation with modern fossils has 

 been noted on the isthmus of Panama and on the Atlantic side of Costa 

 Rica respectively by Dr G. A. Maack and Dr W. M. Gabb f lying uncon- 

 formal)ly on Miocene strata. It occurs up to an elevation of at least 150 

 feet above the sea and constitutes the eroded hills of the low coastal i)lain. 

 Dr J. Crawford ;|: notes the occurrence of recent oyster-bearing beds in 

 Nicaragua. He informs me that they reach an elevation of about 500 

 feet and unconformably succeed Miocene strata. In i:)osition the Matan- 

 zas limestones are represented on the Atlantic side of the isthmus of 

 Tehuantepec l)y Mr J. J. Williams in his geologic section. § 



Most important are the observations of Professor A. Heilprin. where 

 he shows the occurrence of this soft limestone with some extinct fossils 

 over the extensive low plains of northern Yucatan. There, too, the sur- 

 faces are eroded, and the geomorphy is the same as that of the Antilles. 



•Cited befoFP. 



t" IsthiniiM of Diirien Ship Ciinal," cited before, and Gahb's Costa Rica, cited before. 



J Report of the British Association for 1800, p. 812. 



§" Isthmus of Tehuantepec," cited before. 



