Geological Survey of the State of New York. 99 



in deference to the opinion of that author. The first of these 

 synonyms (derived from lemoc) stands in the place of Producta or 

 Productus, a name to which grammarians have objected. 



'' The second genus, Atrypa, (from « privative, and jQvna,) is 

 divided from Spirifer^ and inckides those species which have a 

 short hinge h'ne without a large area, and are either destitute of a 

 foramen, or possess only a small triangular one. They are round- 

 ed shells, and are not furrowed like the typical species of Spirifer ; 

 the internal spiral arms are preserved in some species. Atrypa 

 affinis, and similar striated shells, would form another natural 

 group, in which the internal structure, as well as the general 

 form, is diiferent ; for the spiral appendages, if ever they possess- 

 ed any, do not appear to remain ,• and there are two short cre- 

 nated teeth in the hinge. The species of this division have gene- 

 rally been described as Terehratulce by British authors, but they 

 have acute, not perforated beaks. 



"The genus Orthis (ogOog) is another division of Spirifer, no 

 species of which has heretofore been described in England ; it is 

 distinguished from Spirifer by the long narrow hinge and circular 

 flat form of the striated shells. 



" Our genus Pe/itomen^s is called Delthyris by the Swedes, 

 but we see no reason for altering the name. If we were well 

 assured of the stability of the genus Delthyris, we should remove 

 to it At7ypa galeata, and perhaps one or two other species of 

 Atrypa.^' 



In the survey of the first district, the trap region of Rockland Co. 

 is described as forming a narrow belt, the Palisades, along the 

 Hudson River, from the N. Jersey line to near Haverstraw, thence 

 it ranges off to the northwest, then west, and finally southwest, 

 near the base of the Highlands, and disappears. A branch of it 

 strikes otf westerly, about two miles north of Nyack, towards 

 the Highlands. These ranges are from a quarter to two miles 

 broad, and on the east and north present mural columnar escarp- 

 ments from three to eight hundred feet high, with the usual de- 

 bris at the base ; and the south and west sides usually slope off 

 more gradually. The sandstone beneath is cut through by large 

 and small dikes, and its layers are separated by lateral intrusions 

 of trap. The trap varies from coarse crystalline to very compact 

 greenstone, and from slaty clinkstone to a coarse amygdaloid. 

 The sandstone presents a great variety of color, and of aggrega- 



