38 THE CONDOR VoL. VII is one of the very "facts" about which the geomorphists are now holding the most diverging views. Let me quote a few sentences from a paper by Dr. J. W. Spen- cer as late as May, x898: "It would thus appear that these regions (West Indian region) stood from ten thousand to twelve thousand feet, or in some localities four- teen thousand feet, higher than now;" and further on: "The time of greatest eleva- tion and development of the West Indian continent was during the early Pleisto- cene period." This brings us surely to the time of the origin of bird migration. If conditions were as Prof. Spencer thinks, there is no impossibility of the pro- thonotary warblers' migration route, no matter how it lies across the Gulf of Mex- icoc indicating the way by which they originally immigrated into the United States. Now, Prof. Cooke willprobably answer that there are geologists who hold quite opposite views and that he sides with them, because /f they are right, it would be easy to "refute" Palm?n's theory. But would it? Prof. Cooke speaks of the "central portion" of the Gulf as being involved. There is no necessity for such an assumption, however. Do away with an elevation of twelve thousand feet and let us be satisfied with xoo fathoms? Take any map showing the xoo fathom contour in the Gulf of Mexico and the drowned valleys from the Mississippi to the Tampa, and it will be found that the whole distance from land to land, if it were raised up to this level, would be ?83 miles! Now draw a hypothetical mi- gration route from the northeastern corner of the thus enlarged Yucatan (Cam- peche Bank) northeasterly until it strikes the westwardly extended Florida, and let this line proceed in a northerly to northwesterly direction along the ?oo fathom curve to the mouth of the Mississippi sending 'off side routes up the drowned valley of the Tampa, Suwanee, Appalachieola and other rivers, and you have a route which would explain many features of the migration of the prothonotary warbler, which now are mysterious, and at the same time indicate the way by which it may have originally immigrated into the ?fnited States. It would have been very interesting to have gone into these questions in greater detail, but, unfortunately, time and space are limited. All I wanted to show is that Palmdn's theory cannot be disposed of in this t, ff-hand manner. To stop the error from making further headway in this country will require weightier argu- ments than those I have tried to meet today. Washi?gton, D. C.,./an. 2 3, 19o?q. c It must be distinctly understood that this quotation of Dr. Spencer's views does not iudicate my adoption of them. d An elevation of 600 feet is necessary to bring the loo fathom line on the west side o, ? Florida up to the present sea-level, if the rise is supposed to be horizontal. Dr. W. H. Dall has indicated, however, that the last rise of the peninsula (subsequent to the one I refer to) "elevated the Atlantic border with its reefs more than the gulf shores.', In case of such a tilting it will be sufficient for my purpose to assume a mean elevation of less than a0o feet in order to insure a shoreline ?4 o to ISO miles west of the present one during that period of the Pleistocene when "the rhiuo- ceros, the wild horse, the 11a. ma, the Columbian elephant, the mastodon, the glyptodon. and various enormous tor- toises wandered along the shores of the lakes and through the marshes (of Florida) while the sabre-toothed tiger lay in wait." Surely, the landscape suggested by this quotation might well invite the invasion of the prothonotary warbler in the United States!
