GRAPTOLITES OF NEW YORK, PART 2 IOI 



portion is the outer ends of the thecae while on the contrary the inner ends 

 of the thecae are supported not only by their proximity to the common 

 body but also by the walls of the (in the direct facies) next subjacent 

 theca. Thus when the shale is split, while, owing to the comparatively firm 

 texture of the common body and virgula, the line of fracture nearly always 

 follows the surface of these structures, it usually cuts through the thinner 

 thecal walls, and, as the inner angle of the thecal mouth has been pried up 

 into prominence, it suffers the greatest amount of loss of substance, the 

 resulting form being that with acute "denticles" (the remains of the 

 obliquely truncated theca walls) so frequently seen in the Stockport and 

 Normanskill shales. 



The facies of D. foliaceus Murchison, is typically displayed in 

 the so called " D . prist is Hall" so abundant in the Black Shales of the 

 Hudson Valley. For this reason I shall term it the pristoid facies. As 

 would naturally be inferred from the fact that the normal facies is mainly a 

 result of limestone preservation, while the pristoid facies is mainly a result 

 of shale preservation, intermediate linking facies are by no means common. 

 Still they do occur. Thus in the calcareous Utica shales, just above the 

 Trenton limestone. 



D . a m p 1 e x i c a u 1 i s may be seen acquiring the characters of D . 

 prist is. Also an occasional specimen is seen scattered among the 

 multitudes of pristoid forms in the collection from Magog, Canada. 



Another facies is that exemplified by Dr Emmons's Diplograpsus 

 rugosus. This differs from the preceding only in the fact that, in addi- 

 tion to the oblique truncation of the walls, the furrow bounded posteriorly 

 and vertically by the anterior edges of the walls of the theca next behind 

 (which have been, as shown above, obliquely truncated during the splitting 

 of the shale and which now form a " cliff" the hight of which is the thick- 

 ness of the two thecal walls pressed into contact) and anteriorally and 

 horizontally by the underlying surface of the upper wall of the theca next 

 in front, remains filled by a thin film of shale which gives to the distal por- 

 tions of the thecae an appearance of discontinuity from the proximal 

 portions, thus causing them to simulate a theca of a trapezoidal or subrect- 

 angular form projecting from the main portion of the polypary approxi- 

 mately at a right angle. This may be called the rugosus facies. 



The deceptive appearance mentioned above of oblong or trapezoidal 

 thecae projecting directly outward from the polypary is still more markedly 

 displayed in what I shall call the Climacograptus facies. In this case, owing 

 to different amounts of compression, of polypary resistance etc., the thecae 

 are still more inclined to the plane of the. section and consequently succes- 

 sive pairs are more widely separated, thus permitting the insinuation 

 between them of a thicker film of shale. Owing to their greater inclination 



