MESOZOIC TIME — CRETACEOUS. 821 



4. Laramie Epoch. — 



Unrepresented ? Possibly here the Upper Greensand, Manasquan 

 group of W. B. Clark : 15 to 20 feet thick of greensand, with above, 

 sandy clays and blue marl ; fossiliferous. 



3. MONTAN^A OR RiPLET EPOCH. 



2. Middle Greensand, Rancocas group of Clark : about 45 feet of 

 marl, with as much of yellow sand above ; fossiliferous. 



1. Lower Greensand, ISTavesink group of Clark : 30 to 45 feet of 

 greensand, and above this a red-sand stratum, 100 feet thick; with 

 below Clay marls, 250 to 300 feet. 



2. Colorado Epoch. — 



Unrepresented ? or perhaps the Clay marls. 



1. Dakota Epoch. — 



Baritan group or Plastic clays : thick beds of plastic clay with 

 some interstratified sand-beds ; more sandy above ; 350 feet ; fossil 

 leaves and lignite, especially toward the base (one third of the thick- 

 ness from its base in New Jersey) ; shells rare, and these freshwater 

 of the genus Unto, or brackish-water Gastropods. 



The Raritan group is proved by its remains of plants to be the probable 

 equivalent of the Dakota of the Continental Interior ; and the Lower Green- 

 sand group, by its fossils, as well brought out by Whitfield, to be the equiva- 

 lent of the Ripley group of the Gulf border. Whitfield refers to the same group, 

 but doubtingly, the nearly unfossiliferous Clay marls which lie below it. The 

 Upper Greensand group graduates, without a break in the stratification, into 

 the overlying Eocene Tertiary, as if its formation were, like the Upper Lara- 

 mie, the closing work of the Cretaceous period. If not so, the Laramie epoch 

 is not represented on the Atlantic border. 



The Lower Greensand is the most fossiliferous of the series. Whitfield 

 has described from it 19 species of Cephalopods, 127 of Gastropods, 155 of 

 Lamellibranchs, and 2 of Brachiopods, or a total of 303 species, against 47, 

 under the same tribes, from the Middle and Upper Greensand groups. Not- 

 withstanding the unbroken passage of the Upper Greensand group into the 

 Eocene Tertiary, out of the 79 Eocene species of Mollusks described by 

 Whitfield, none occurs in the underlying Cretaceous. 



The clay of the Raritan group is partly pure white clay, but it varies to 

 gray, yellow, and red in color, owing to traces of iron oxide, and in some 

 places to black in consequence of disseminated fragments of lignite which 

 had been gathered from some lignitic bed. In general, it is not laminated 

 clay, like that of nearly all river valleys, but a massive clay free from lami- 

 nation and of remarkable purity. The best of it has great value for the 

 manufacture of fine pottery and other purposes. 



The Raritan formation, with its massive clays of various colors, occurs 



