GRAPTOLITES OF NEW VOUK, PART 2 36 1 



e Diplograptus (sp. mulct. ) Emmons. 1856 



Am. Geol. v. 1, pt _'. p. 236— 37, t. r, fig. 3 



" It is thin, olive-green and foliaceous, but its characters too obscure to 

 be determined with certainty." 



In this opinion of Emmons I concur. 



From our own observations on the various preservation facies of the 

 Diplograpti, we fully concur in Gurley's views on the invalidity of Emmons's 

 species. In regard to the supposed characters of D . secalinus it seems 

 that preceding- authors have not taken sufficient notice of the extreme 

 distortion that all of the specimens in the Hoosic Falls slates have under- 

 gone by the position of the slate in the zone of extensive folding in the 

 Taconic mountains. We present on plate 25 the tracings of three specimens 

 from one slab, showing clearly the effect of longitudinal stretching on some 

 specimens [fig. 7] and that of endwise compression on specimens lying at 

 right angles to the former | fig. 9]. In the stretched specimen the number 

 of thecae has sunk to 5 in io mm ( 13 in 1 inch) and in the other risen to 

 11 (28 in 1 inch) ; the average (8, resp. 20) which is shown by the third 

 specimen, inclined about 45 to the direction of the principal strain in the 

 slate, is that of a D . f o 1 i a c e u s of the group of D. foliaceus var. 

 i n c i s u s , with which the Hoosic specimens also agree in their average 

 dimensions — the great diversities in the length and width of the rhabdo- 

 somes also being caused by orogenic forces — and, as far as it can be made 

 out, in the form of the thecae. The extreme and misleading width of some 

 rhabdosomes is due to the combined action of endwise compression and 

 strong flattening. 



Diplograptus (Glyptograptus) amplexicaulis (Hall) 



Plate 25, figures 10-13 



Graptolithus amplexicaule Hall. Pal. N. Y. 1847. r : 79, pi. 26, fig. 11a, b 

 Diplograpsus amplexicaule Emmons. Amer. Geol. 1856. p. 336. pi. 7, 



fig. 11a, b 

 Graptolithus amplexicaule Hall. N. Y. State Cab. Nat. Hist. 20th An. Rep 't. 



1868. pi. 3, fig. 6. 7 



