THE NORMANSKILL GRAPTOLITE FAUNA 279 



Diplograptus foliaceus var. incisus 



Diplograptus foliaceus Murchison, var. acutus Lapworth 



Diplograptus foliaceus 



Dictyonema 



Glossograptus quadrimucronatus Hall, var. cornutus 



Lasiograptus mucronatus Hall 



Leptobolus walcotti 



Nemagraptus exilis Lapworth 



Nemagraptus exilis Lapworth, var. linearis 



Nemagraptus gracilis Hall 



Phycograptus laevis (Graptolithus laevis Hall) 



Retiograptus eucharis Hall 



Triarthrus becki 



An interesting feature of a number of these species is their 

 occurrence in original colonies, or synrhabdosomes. Several species 

 show synrhabdosomes which have not heretofore been observed. 

 All of the above listed forms occur in fresh material, are very dis- 

 tinct, and apparently not at all distorted, or flattened. The grap- 

 tolites occur in all parts of the formation from top to bottom. 



The Black River formation beneath the Athens shale is made 

 up of dark to black coarsely crystalline limestone and marble, 250 

 feet thick. It contains several distinct bands of marble between 

 the middle and the top. One occurs at the top. The marble is 

 of a smoky-gray color, rather coarsely crystallized, and fossiliferous. 

 The bed near the middle is about 6 feet thick, the other beds some- 

 what less. The mass as a whole, except the lower part, appears 

 to be a coral reef on which flourished crinoids, bryozoa, brachiopods, 

 gastropods, and, in the lower part, orthoceratites. The lower part 

 of the formation is more or less sihceous and cherty, which on 

 weathering produces knots over the surface. The Black River was 

 laid down on an unevenly eroded surface of dove-colored limestone, 

 the Lowville (Birdseye). The hiatus here shown is well marked. 

 A sharp line can be drawn between the coarse, dark, impure Hme- 

 stone above and the pure fine-grained, dove-colored limestone 

 beneath. The Lowville contains Tetradium cellulosum in abun- 

 dance, and near the bottom large, coiled shells. The formation is 

 about 50 feet thick and terminates in a very coarse, brecciated lime- 

 stone conglomerate, which separates it from the Chazy below. 



