74 The Upper Cretaceous Deposits of Maryland 



The general make-up of the fauna indicates a muddy bottom covered by 

 quiet waters, certainly not more than 50 fathoms in depth. However, it is 

 by no means an estuarine fauna but one that lived in the open sea. There 

 was, probably, free communication with the inshore life of the Gulf 

 region, but there may have been a barrier, possibly a volume of fresh 

 water, which shut off some of the New Jersey shore life. The waters were 

 doubtless warmer and much more uniform in temperature, and environ- 

 mental conditions, as a whole, more favorable to molluscan life than 

 they are off the Maryland coast to-day. 



The Monmouth formation is the equivalent of the Peedee beds of North 

 and South Carolina and the upper part of the Ripley and its equivalent, 

 the Selma chalk of the Gulf. The forms point to the Lower Senonian 

 (Emscherian) age of the beds. 



The Rancocas Formation 



The Rancocas formation, so named by the writer ' from Rancocas Creek, 

 New Jersey, where the deposits of this horizon are extensively developed, 

 has not been found to outcrop within the limits of the state, although it 

 occurs in Delaware near the Maryland Line and in all probability occurs 

 in Maryland beneath the cover of the Tertiary formations. Its separation 

 from the underlying deposits under the name of the Middle Marl in 

 New Jersey was early recognized. The subdivisions of this formation 

 into the Homerstown marl and Vincentown sand in New Jersey become 

 gradually obscured to the southward, the marl even appearing within 

 or at the top of the lime sands. 



The Rancocas formation overlies the Monmouth unconformably and 

 its line of contact is generally sharply defined. 



It contains a fauna very distinct from those of the underlying Upper 

 Cretaceous formations. The faunas of the Magothy, Matawan, and Mon- 

 mouth are much more closely allied with one another than with the 

 Rancocas formation in which quite distinct faunal elements make their 

 appearance. No deposits of equivalent age have heen recognized in the 



1 Clark, Wm. Bullock, Jour. Geol., vol. ii, p. 166, 1894. 



