480 NEW YOKK STATK MUvSEUM 



Another advantage of the shale material, of equal importance to the 

 stratigrapher and the student of the phylogeny of the graptolites, is the fact 

 that the graptolite shales, being slow deposits, frequently contain rapidly 

 changing graptolite faunas within a very limited thickness of rock, as in the 

 Deep kill section which has furnished the principal material for this memoir. 



As stated before, the flattened shale material allows the elucidation of 

 but very meager facts bearing on the internal structure of the graptolites. 

 Sometimes, however, these bodies became centers of crystallization, mostly of 

 pyrite, and have thus been protected from flattening and crushing forces. 

 Such pyritized specimens have been used for the preparation of sections 

 by Tomquist [see p.476]. A layer of graptolite bed 2 in the Deep kill 

 section contains numerous pyrite nodules, mostly with specimens of 

 Phyllograptus ilicifolius; and the writer has been able to obtain 

 from thin sections of these, certain facts as to the structure of the stipes and 

 of their periderm. 



The best results, however, have been acquired by the study of the 

 graptolites which are sometimes found embedded in limestone, calcareous 

 shale or chert. By means of sections uncompressed specimens which were 

 preserved in more or less calcareous beds, have been studied by Perner 

 (Monograptus and Retiolites), Gurich (also Monograptus) and by Holm 

 (Phyllograptus). 



In calcareous or flinty beds the graptolites can be further etched out 

 with acids without crumbling to pieces, as those of argillaceous shale will 

 do under such treatment. This method was first applied by Giimbel [1878], 

 but has been brought to great perfection by Holm and specially by Wiman.^ 



Limestone material was found the simplest to handle, and muriatic acid 

 in diiferent states of solution or milder solvents such as acetic acid, gave good 



» Dr Wiman has published an interesting account of his preparative methods in his 

 paper " Uber die Graptoliten" [1895] and in the " Structure of the Graptolites" [1896J. 

 His work has been reviewed in the American Oeologist [1896] by Clarke, and in the 

 American Naturalist [1898] by Ruedemann. 



