Frazer.] 6b4z [March 19, 



the lumbar diapophyses. A few years ago I defined a genus, based on 

 several species from the Miocene of Maryland, in which the lumbar 

 diapophyses are spiniform. Supposing the Priscodelpliinus harlani of 

 Leidy to possess the same character I retained the same generic name for 

 the Maryland species. After an examination of considerable material from 

 the New Jersey locality, including bones of P. Jiarlanii, I have failed 

 to observe a single species with the spinous processes alluded to. It thus 

 becomes evident that Priscodelphinus must be retained for the species 

 termed by me Ti'etospTiys, while that for which I retained the name Pr is- 

 codelphimcs must receive a new one. For this I propose BelospJiys with 

 B. spinosus, Cope, as type, and B. atropms, B. conradi and B. stenus as 

 species. At the same time I add that the presence of Ixacanthus coelos- 

 pondylus, Cope, in the New Jersey Miocene mentioned in Cook's Geologi- 

 cal Survey of New Jersey by the writer, is doubtful. 

 Total number of species, thirty-three. 



ORIGIN OF THE LOWER SILURIAN LIMONITES OF YORK 

 AND ADAMS COUNTIES. 



By Persipor Frazer, Jr. 



{Bead before tlie American Philosophical Society, March 19, 1875.) 



The three great deposits of Lower Silurian limestone which occur in 

 this State, are : 1st. That of the Chester Valley which begins at Willow 

 Grove, in Montgomery county, and terminates about a mile west of 

 Minerstown, in Lancaster county ; 2d. The great Lancaster and York 

 county basin which, commencing about a mile northeast of Morgantown, 

 crosses the Susquehanna River in two prongs, the longer (most northerly) 

 of which terminates almost on Mason and Dixon's line in the southeast 

 corner of Adams county; and 3d. The great valley, par excellence, which 

 enters the State at Easton on the Delaware River, and passes into Mary- 

 land in a wide belt, which stretches fifteen miles east and the same dis- 

 tance west of Middleburg, Franklin county. 



Accompanying all these limestone basins are belts of iron ore which 

 crop out at tolerably uniform distances below their edges. In the still 

 lower measures of the Silurian, and above the Potsdam sandstone, are 

 other belts of ore entirely disconnected from the limestone ores. 



In the first Report of the Geology of Pennsylvania (Vol. I, p. 218), it is 

 stated of the Rathfon Ore Banks of Lancaster county, that in this, as in 

 most of the other iron veins connected with the magnesian limestones, 



