THE ALUM BLUFF SECTION. 157 



is little else as far as the eye can reach. Camp was made at the north 

 end of the bluff. A section was most carefully made at the highest ex- 

 posure, with steel tape, portable transit and stadia, a small baseline and 

 triangulation being measured for that purpose : the weathered surface 

 of the strata shaved clean with a spade and photographed ; some of the 

 fossil plants, being too frail to transport, were photographed in situ ; a 

 general panorama of the bluff was photographed from the opposite bank 

 of the river, and some fossils with a series of rocks collected for analysis 

 and study. The large collection obtained here in 1890 by Mr Frank 

 Burns rendered it unnecessary to spend much time in searching for 

 fossils. 



The section was taken at the part of the bluff indicated by A-B on 

 the sketch-map. 



Section at Alum Bluff. 



1. Superficial sands 8} feet. 



2. Red clay % " 



3. Reddish and yellowish streaked sands 66 " 



4. Aluminous clay 24 ' ' 



5. Chesapeake gray marl 35 " 



6. Alum bluff" sands with streaks of clay 21^ " 



7. Hard Chipola marl to water (variable) 3} " 



Total thickness above water 160| *' 



The composition in detail of these several beds is as follows : 



Number 1. — Pale 3'ellowish gray incoherent sand. 



Number 2. — Hard reddish clay weathering with vertical face. 



Number 3. — Streaky yellowish and reddish sands with small little- 

 worn gravel, of siliceous character, mixed with it. Near the lower third 

 a few obscure impressions, possibly representing fossils, were observed 

 by Mr Stanley-Brown. The lower 8 feet of the sands is more or less 

 loamy from admixture with underlying clay. They are distinctly strati- 

 fied in conformity with the other beds of the bluff. 



Number 4. — Tough gray aluminous clay weathering nearly vertical 

 with a very few fragments of vegetable matter in it. and some obscure 

 indications of gastropod and bivalve fossils, the shells entirely dissolved 

 and represented chiefly by color-marks in the clay. The appellation of 

 " lignitic," heretofore applied to this clay on the authority of Mr John- 

 son, cannot be regarded as justified, as the amount of phytogene ma- 

 terial is trifling. The fossils may have been marine or fresh water. No 

 satisfactory evidence is afforded by their faint traces, as observed by us. 



Number 5. — Bluish gray tough clayey marl replete with characteristic 

 Chesapeake fossils, especially Mactra cohgesta. The upper six inches is 

 discolored by iron oxide, derived from the water oozing from the bed 

 above, which has also dissolved the shells, leaving only cavities. Toward 



