LAND SUHMEHGENCE IX THE PLIOCENE. 127 



tlie metaniorpbic rocks, of Paleozoic limestones or of the im])urities of Ter- 

 tiary limestones. The old land snrfaces furnished an al)undance of such 

 material to the (exclusion of calcareous organisms, for in the formation 

 no marine life has l)een found. The Lafayette formation was deposited 

 on the eroded surfaces of all such formations as occur along the coast of 

 the continent of geoh^iric date from the Archean time to the later ]\Iio- 

 cene i)criod. Fn the West Indies the physical conditions were different 

 from those of the continent, for there were few islands to furnish sedi- 

 ments and so the Lafayette loams were replaced by the Matanzas lime- 

 stones. That the lands in the Antilles would have supplied such mate- 

 rials if they had been more elevated is proved by later events in the 

 geology of that region. Thus in a visit to the West Lidies the writer 

 was not prepared for the identification of accumulations so dissimilar, 

 but on the discovery of the key it was found that such differences should 

 have occurred. 



The Antillean region may be too great an area to bring within the 

 scope of the gentle epeirogenic movements, but beyond the limit of the 

 orographic disturbances the deformation of the earth's crust over the vast 

 region from New Jersey to Mexico shows undulations in the coastal 

 plain of hardly a thousand feet < from 100 feet, above tide, near Cape 

 Hatteras, to 800 feet in South Carolina, 250 feet in Arkansas and 1,000 

 feet on the Rio Grande). Only on approaching the vicinity of the isth- 

 mus of Tehuantepec do the undulations become involved in the recent 

 and great mountain movements. The elevations of the Matanzas lime- 

 stones from the Windward islands to Central America seem to be only 

 affected by gentle undulations until reaching the zone of transverse but 

 recent mountain u[)lifts. Herein lie some difficult and unsolved prob- 

 lems. Except in the region of the Pacific barriers and one or two other 

 localities the evidences of moderate terrestrial undulations is markedly 

 shown in the character of the submerged valle3^s. From the various 

 considerations set forth the conclusion is reached that the Matanzas epoch 

 (about equivalent to the Lafayette) rei)resented a general submergence 

 below the present altitude, not only of the costal plain to. from 100 to 

 1,000 feet, but that tlie Antillean lands at the end of the Pliocene period 

 were depressed so that only a few islands remained at altitudes from 

 100 to 1,100 feet lower than today. JUit at that time there was also an- 

 other variation in the to[)ogra})hy, for the mountains had not their axes 

 so highly elevated above their flanks as they now are, as pointed out on 

 page 128, and as demonstrated by the character of the modern erosion of 

 the recently elevated bases of the mountain valleys. 



The epeirogenic movements may not have been quite synchronous ; 

 perhaps beginning a little later in the north than farther south and also 



XVni-lUi.i.. (iy.ni. Hoc. Am.. Vol. 0. 1«'J4. 



