THE ALTAMAHA GRIT REGION OF GEORGIA 11 



ably has no counterpart in any other part of the world. In its 

 typical development it extends from about the mouth of the 

 Hudson River uninterruptedly to the Rio Grande, and up the 

 Mississippi valley to southern Illinois. Most of Long Island, 

 Cape Cod, and the southern islands of New England also belong 

 to the coastal plain, strictly speaking, but as these extreme 

 northeastern portions are mostly covered with glacial drift, and 

 otherwise anomalous, they are not usually treated with the rest. 

 Just what becomes of the coastal plain at its other end, in Mexico, 

 is not definitely known, but it probably does not extend very far 

 into that country. The boundary between the coastal plain 

 and the Piedmont region which adjoins it all along the Atlantic 

 slope is very distinct and unmistakable, as has already been 

 pointed out, 1 and is known as the fall -line. 



Practically the whole of the coastal plain is or has been covered 

 with a superficial formation known as the Lafayette, believed to 

 be of Pliocene age, and much of that is in turn overlaid with a 

 Pleistocene formation, the Columbia. The importance of these 

 two formations from a phytogeographical standpoint has been 

 quite generally overlooked. They not only constitute the 

 present soils of the coastal plain, making it difficult to trace the 

 older formations beneath except by their topography, but they 

 also show that the present flora of that region must be of very 

 recent origin, differing greatly in this respect from that of the 

 older regions just mentioned. 



4. Subtropical Florida. The southern extremity of Florida, 

 including the Everglades and a good deal of contiguous territory, 

 is sometimes regarded as an extension of the coastal plain and 

 sometimes as a distinct province. It is believed to be of 

 Pleistocene age, and is certainly not covered by the superficial 

 formations above mentioned. This alone would be enough to 

 make its soil and flora very different from that of the genuine 

 coastal plain, but it happens also that this is the only part of 

 the Eastern United States free from frost, so it is an open 

 question whether the peculiar flora of this region (said to 

 resemble that of the neighboring Antilles as much as it does 



1 Bull. Torrey Club 31: 10. 1904; Rhodora 7: 69. 1905. 



