1 66 THE JOURNAL OF GEOLOGY. 



The formation has a rather constant thickness of lOO feet. 



Rancocas formation (Middle Marl Bed). — The Middle Marl 

 Bed is not as prominent a feature in Monmouth county where the 

 type localities for the other formations are found as farther south- 

 ward. The Rancocas Creek in Burlington county cuts through 

 the Middle Marl Bed exposing a full sequence of the deposits of 

 that formation, while in the neighboring area extensive exposures 

 of the strata are found: 



The formation is largely a greensand, although much more 

 highly glauconitic in the lower than in the upper half of the for- 

 mation. Although the lower half is largely a pure greensand, 

 it becomes in some portions of the state very argillaceous 

 toward the base, forming the so-called "chocolate marl," while 

 toward the top it becomes crowded with shells, the upper two 

 feet characterized by the presence of Terebrahila Harlani, the 

 most persistent fossiliferous zone in the state. The upper half 

 of the formation is highly calcareous, frequently appearing as 

 limestone ledges, known as "yellow limestone," and often contain- 

 ing as much as 8o per cent, of carbonate of lime. It is extremely 

 fossiliferous, and has afforded many beautifully preserved speci- 

 mens of Bryozoa, Echinodermata and Foraminifera. The fossils 

 are, in the main, different from those in the underlying forma- 

 tions. 



The strata reach a thickness of about 45 feet. 



Manasqiian formation (Lower portion of the Upper Marl Bed) . — 

 The name Manasquan Marl was in an earlier publication made to 

 include the Yellow Sand, together with the "green sand" and "ash 

 marl" of the Upper Marl Bed of Professor Cook. For that hori- 

 zon the term Manasquan formation is retained. It is typically 

 developed in the valley of the Manasquan River and its tribu- 

 taries. 



Like the preceding formation it is essentially a greensand 

 throughout, although distinctly quartzose in the lower part, and 

 at times argillaceous in the upper layers. The fossils so far as 

 observed are confined exclusively to the more highly greensand 

 member, but the number of species is not large. The high per- 



