Page:Popular Science Monthly Volume 76.djvu/412

408 swarming is not due to tidal influences, and now the great question is—what does cause this remarkable response, for it appears to be some form of energy to which we are ourselves not sensitive.

Dr. T. Wayland Vaughan, of Washington, finds that the line of the Florida Keys from Soldier's Key to the southeastern corner of Big Pine Key is composed of elevated coral-reef rock. The northern end of Soldier's Key and all keys to the northward of it are composed of quartz-bearing sands mingled with broken shells. The keys from Key West to Big Pine Key, with the exception of the southeastern corner of the latter, are composed of limestone mud which long ago was elevated above the sea and changed into rock, so that now one sees a net-work of old mud-cracks in the rocky floor of the pine forest. On the continental side of the line of coral-reef keys and extending transversely to them are long shoals formed by the settling of lime mud in the slack water between the currents which flow in and out with the tides through openings between keys. These shoals become covered with mangroves, and thus finally elevated above the surface of the sea. There are many other interesting geological observations made by Dr. Vaughan which limitations of space prevent us from reviewing.

In addition to his studies of the geology of the reef's, he is making