No. 136.] 59 



(Fig. 21, No. 4), Belthyris macropleura (Fig. 22, No. 1), Merista 

 Icevis (Fig. 22, No. 2), Eatonia medialis (Fig. 22, No. 4), and the 

 two StrophomeTKB (Fig. 23). There are several trilobites, and 

 some very beautiful and perfect encrinites have been found in 

 these strata in Schoharie and Herkimer counties. 

 The chief of the Helderberg sandstones is 



THE ORISKANY SANDSTONE, 



which overlies the Lower Helderberg group, is, at Oriskany Falls, 

 whence it derives its name, a light coarse sandstone about twenty 

 feet thick. In localities further west, it is sometimes, as at the 

 falls of the Chittenango creek and at Split Rock near Syracuse, 

 either wanting or represented only by a few inches of dark sandy 

 rock; sometimes, as between Elbridge and Skaneateles, thirty 

 feet thick ; and in other localities, of various intermediate thick- 

 nesses. Near Schoharie, it contains some lime with its sand, and 

 is light colored ; in some parts of the Helderberg, as near Clarks- 

 ville and Knoxville, it is only a foot or two thick, a hard black 

 stratum full of fossils. In Pennsylvania, it is from 150 to 300 

 feet in thickness, and contains the same organic remains which 

 are found in it in New- York. But the finest fossils yet dis- 

 covered in it are near Cumberland in Maryland, wiiere the crumb- 

 ling texture of the rock causes it to decompose, often leaving the 

 shells as perfectly free from adhering matter as those of the sea- 

 shore ; so that every detail of internal structure, as well as 

 external form, is perfectly seen. 



The fossils of this rock are numerous, some sixty species being 

 described in Professor Hall's third volume. Among the most 

 characteristic are those shown in figures 24-25. The forms in 

 Fig. 25 are internal casts, or moulds of the interior of the shells, 

 formed by the sand which filled them ; the substance of the shell 

 itself having decomposed. These " casts " ^ are very abundant, 

 and give rise in the raind of unlearned observers to many fanci- 

 ful resemblances, such as "butterflies," "colts-tracks," etc. etc. 



Above the Oriskany sandstone, in the Helderberg region, is a 

 mass of sandy slate or shale, often more than fifty feet thick ; 

 but it is not known west of Herkimer county. In Pennsylvania, 

 it is seen from the State line to the Water-gap. It forms, by 

 decomposing, a poor soil ; and is equally barren in fossils, the 

 only form known being what is called the Cocktail fucoid, sup- 

 posed to be the remains of a marine plant, the form of which re- 



