GRAPTOLITES OF NEW YORK. PART 1 481 



results in dissolving the matrix. Strongly argillaceous marl slates were first 

 treated with acetic acid, which dissolves the lime content, and then the 

 graptolites were brought out with hydrofluoric acid. In silicious rocks, mostl)- 

 chert masses, graptolites have been freed with concentrated hydrofluoric acid. 



The isolated graptolites have been decolored by Holm and Wiman in 

 different ways. Wiman used first Schultze's maceration medium, which is a 

 solution of calcium chlorate in nitric acid, but later substituted for it eau de 

 Javelle or potassium hypochlorite, because Schultze's medium is often too 

 harsh. The specimens were then cleared with chloroform or other clearing 

 fluids and mounted in Canada balsam. Where this method could not be 

 used on account of the thickness of the periderm, they were prepared for the 

 microtome according to the methods used by zoologists. 



The methods of illustration of graptolites have also been gi'adually 

 improved. Minute isolated specimens and thin sections have been drawn 

 with the camera lucida by Holm and Wiman and thus accurate representa- 

 tions obtained. As the specific distinctions of the graptolites have frequently 

 to be sought in minute details, such as the inclination and closeness of 

 arrangement of thecae, the former method of free-hand drawing with its 

 unavoidable idealization of the figures, is no longer sufficient to bring out the 

 crucial characters with the desired accuracy. Fortunately the shale material 

 as a rule retains just enough relief to permit its being drawn with the camera 

 lucida or even being photographed as Barrois has done. Van Ingen has also 

 successfully photographed graptolites of the St John group and then used the 

 photograph for tracing [Matthew 1895]. By his kind assistance I have been 

 enabled to bring out characters photographically which were visible to but 

 few observers. 



Lapworth has had constructed, for the illustration of the British 

 graptolites in the monograph now under preparation, a horizontal microscope 

 with attached camera lucida. By means of this arrangement the specimens 

 can be enlarged with the least possible slanting to five times natuial 

 size. The drawings have then been shaded and reduced by photographic 



