Page:Popular Science Monthly Volume 76.djvu/592

588 Nature is very kind in preparing fossils for us. The Onondaga limestone, at the Falls of the Ohio, although only a few feet in thickness, has yielded seven hundred or more species of exquisitely preserved fossils. Examine the freshly quarried limestone and you may be able to crack out perhaps two dozen species of poorly preserved material, but go to the neighboring field where solution of the limestone and silicification of its contained fossils has occurred, and a host of beautiful forms awaits you. Strata., which under ordinary circumstances would yield very poor fossils, can, if silicification has commenced, be made to afford excellent specimens. By exposure to the weather for a year or so, the silicification can be advanced to such a stage that etching with acid will free the fossils. The beautiful etched material from the New Scotland of New York is a familiar example of this style of preparatory work. Most of the Cambrian and Ordovician formations of the Appalachian Valley yield shells which, as they occur in the limestone, are almost impossible as subjects for study, but as silicified pseudomorphs, all the beauty and detail of the original shell are reproduced.

Thin sections are a valuable aid in identifying the merest fragment of certain classes of organisms, and their use here is indispensable. A thin section of an otherwise undeterminable fragment of a Cambrian protremate brachiopod will distinguish the horizon. Other methods of preparation and study might be mentioned, but time forbids, although I can not refrain from speaking of the several whitening processes. The use of a coating of ammonium chloride or anilin chloride on fossils for photographic purposes is well known, but the excellent results obtained from the use of the same process in the study of poor material may not be so apparent to all. A trilobite indistinctly outlined in the rock under ordinary circumstances, flashes into bold relief when covered with the ivory white film of ammonium chloride. Casts and molds of fossils too indistinct to show any structure ordinarily, will reveal many characters when so whitened. Recently occasion arose to study a species of Cambrian phyllopod which had already been described and figured. The specimen was practically nothing but a film upon the rock, and apparently the last word had been said upon it. It was suggested that the specimen be whitened and then photographed with the sun's rays nearly parallel to its surface. The result was most gratifying as structures which could not be proved to exist by the aid of the eye alone, came into plain view in the negative. All these various methods of preparation and study make available a vast amount of material which formerly was thought too imperfect to be fully considered in determining the adequacy of the record, hence the great value of such methods to the paleontologist is obvious.

The real adequacy of the record, if it might be so called, lies in the