Page:Condor12(1).djvu/12

 12 VOL. XII FOSSIL BIRDS FROM THE QUATERNARY OF SOUTHERN CALIFORNIA By LOYE HOLMES MILLER ROBABLY no more unique or interesting deposit of vertebrate fossils was ever made knovn to science than the Quaternary beds recently designated by Dr. J. C. Merriam "The Rancho La Brea Formation." Almost certainly no deposit of similar area has yielded greater numbers of that group so sparingly pre- served to the paleontologist--the class Aves. Ten miles west from the center of Los Angeles, California, the great acreage of Rancho La Brea, one time grain and stock ranch, has within a decade or so assumed 'a new value. The evidence exposed there from Quaternary time has recently been interpreted and a forest of oil derricks has sprung up, to yield a million dollars' worth of oil annually. But the particular kind of evidence indicat- ing the deep-lying oil strata becomes of interest to the scientist because of its long exposure and the fact that man was not the only animal persistently heedless of its true nature. The heavy asphalt-bearing oil, forced to the surface thru overlying strata, accumulated in the natural depressions as small lakelets of oil which, as the more volatile constituents evaporated, became masses of plastic and marvelously tenaceous, tar-like substance. These tar-pools, when undisturbed, possess the mirror-like surface of water and, especially at night or in the half light of dusk, would readily be mistaken for such; yet the bird whose wing-tip touches the innocent looking surface, or whose foot plashes into its margin, is as surely doomed as tho caught in the jaws of a more active enemy. In rainy season the depression becomes further filled by the addi- tion of a super-stratum of water which may cover the tar surface to a depth of several inches, remaining fairly pure water for some time before it becomes polluted by the rise of the lighter constituents of the oil layer. Animals, small and large, wade rashly into the tre ':aerous trap thus baited with that rare luxury of the region, water. The struggling victim becomes again bait for the predatory forms and all in turn tempt the final captive, the carrion feeder. Today, as in ages past, the trap is at work. Barn Owls, Great Blue Herons, Meadowlarks and other birds have been noticed in the surface pools, still in the flesh. The tar pools of Quaternary time have been by the .slow process of natural distillation, converted into masses of stiff asphalt seamed here and there by softer seepage cracks like the resin pockets of raw pine timber. This matrix is quite preservatiye and fairly easy to work, and specimens taken from these beds are easily cleaned with gasoline, tho they retain the dark discoloration of the asphalt. It has been the writer's privilege thru the courtesy of the ranch owners, to collect somewhat in this. interesting locality. Also the whole of the bird material in the collections of the University of California has been placed at his disposal by Professor Merriam for careful examination. The task of describing this great mass of material is little more than begun, but enough has been determined to show the importance of the field. Two papers descriptive of three new species of birds were pubtisht in the University Press x. To these the reader is referred for detailed descriptions; the aim here is to present some of the points of more general interest. Much has been said of the remarkable mammalian forms of the Quaternary, remarkable no more for peculiarity of form than for peculiarity of distribution as It Publ. Univ. Calif., Geology, vol. 5, nos. 19 & 20.