GRAPTOLITES OF NEW YORK, PART 1 



541 



layer and the columnar layer [see fig. 13, 11]. The last two are distinctly 

 composed of calcite crystals. As these two zones are correlatives in their 

 -width — the one is in some places entirely replaced by the other — and 

 as they are separated by a jagged line, corresponding to the sections of crys- 

 tals, it is to be inferred that they result from a single deposit of fibrous 

 calcite crystals, which, being slightly curved, show in the angular zone 

 their sections and in the columnar zone their lateral faces. Bands of 

 broAvn pigment appear at irregular intervals in the angular zone. No traces 



^^=?s:^^K_^<C^> 



Fig. 14: 



Fig. 13, H Dichograptus sp. Thin sections through walls of pyi-itized 

 specimens. Deep kill. x215 



of an exterior or interior epidermis have been observed in any of the sections, 

 but it is quite possible that these, if present, are, on account of their thinness, 

 entirely concealed b}' the pyrite matrix. 



It can be considered however as established by Perner's and AViman's 

 observations that there existed an " epidermis " besides the principal black 

 wall. In other forms, as in numerous species of Lasiograptus, which the 

 writer has collected in the Trenton graptolite beds, and which will be 

 described in the next memoir, the thm epidermal layer and the principal one, 

 which there is dissolved into a network of fibers, can be readily discerned. 



The angular and columnar layers can not be considered layers of the 

 periderm of the graptolites, though they may correspond to some part of 



