L. C. JOHNSON — THE NITA CREVASSE. 25 



wells, in which the water often rises considerably and sometimes, in low places, over- 

 flows. 



It would appear that durinsj the earlier part of the period of deposition of the 

 Pontchartrain clays the great river embouched, in high-water stages, at the last bluffs 

 "or in the vicinity of Baton Eouge, or perhaps as far up as Port Hudson, and, then as 

 now,* the current seems to have tended eastward along the coast. From the topmost 

 layers at both these localities the date of the period may be definitely fixed in geologic 

 chronology as that of the glacial period ; for there may be seen a modification of loess 

 identified by position and stratigraphic continuity with the calcareous and fossiliferous 

 •loess of Natchez and Vicksburg ; and by like continuit}^ the same loess may be identi- 

 fied and traced eastward indefinitely, though thinning out at the same time to con- 

 stitute the brick loams of the lake parishes and Pearl river. No fossils are found in 

 this modification of the loess any more than in the Pontchartrain clays, and for a 

 similar reason, this reason being exemplified in the recent break at Nita, with the 

 attendant disjilacement of a distinctive fauna. Beneath the loess and corresponding 

 loams lies the type and homologue of the Pontchartrain clays, viz., the ''pinnacle 

 sands" and brownish claj's with calcareous "puppets" so well exposed at Port 

 Hickey, Port Hudson and Bayou Sara. These represent the Port Hudson formation 

 of Hilgard, and indicate the Pontchartrain clays to be equivalent to the Port Hudson. 



It is interesting to note that no fossils have been discovered near the axis of de- 

 velopment of the Pontchartrain clays along the old coast line extending southeastward 

 from Baton Kouge, except in the very lowest silts where lie the remains of the forests 

 overwhelmed by the glacial floods. At the most eastern and southern extension of 

 the formation, however, where the icy and "hiuddy cui-rents mixed with the warm 

 waters of the Gulf, marine shells would naturally be looked for ; and in fact artesian 

 well borings have brought up remains of living marine moUusca in many places. 

 These borings show the clays to have a thickness of about 100 feet. 



And thus the Nita crevasse, with its floods of muddy water seeking an outlet directly 

 into Mississippi sound, and with the destruction or displacement of aquatic life over a 

 large area, illustrates an episode in the development of the lower Mississippi region 

 such as has been enacted more than once in the past, and illustrates at the same time 

 the manner in which the development of the region has been accomplished. In all 

 the series of events and deposits, from the first stages of the Port Hudson and Pont- 

 chartrain to the uppermost clays of these formations and the sands and gravels at the 

 base of the loess, to the stages of the loess at Bayou Sara, of the loam at Port Hickey 

 and Baton Rouge, of the brick clays on Amite and Pearl rivers, and of the Biloxi 

 sands, down to the effects of the Nita crevasse, the method, the system and the agent 

 have been but one ; the dates of action and doubtless the degrees of energy have 

 varied, but the source of the material and power has always been and is to-day the 

 same — the great river from the north. 



The next paper on the programme was the following : 



AN OLD LAKE BOTTOM. 

 BY L. E. niCKS. 



Primitive structural forms are so generally replaced by forms of erosion upon the 

 land surfaces of the earth that it is a matter of some surprise to encounter a truly 

 primitive and unmodified surface of construction. Especially in the region of the 



IV— Bull. Geol. Soc. Am., Vol 2, 1890. 



