588 THE POPULAR SCIENCE MONTHLY 



Nature is very kind in preparing fossils for us. The Onondaga 

 limestone, at the Falls of the Ohio, although only a few feet in thick- 

 ness, 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 lime- 

 stone, 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 sug- 

 gested 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 



