20 ON THE GEOLOGY OF LOWER LOUISIANA 



Not fill- below the summit of the hioh ridw mentioned as existin" to the south- 



ward of Prospect Hill, we find large 



fragments 



of a pinkish sandstone, such as 



sometimes occurs, likewise, in the Drift hills of South Mississippi. The quartz 

 grains are well rounded, and mingled with grains of whitish pipe-clay, while the 

 cement is siliceous. It appears to occur in a ledge fifteen to eighteen inches thick, 

 overlaid by a bluish or greenish clay, the outcrop of which I could not discover. 



This is by many feet the highest point at which I have found, on the Louisiana 

 coast, materials belonging, apparently, to the Drift. At the foot of this ridge are 

 the most characteristic outcrops of the Orange Sand, near Chouteau's upper pit; 

 but higher up on the slope, we find the same doubtful sand as on Prospect Hill; not, 

 however, any of the greenish calcareous clay, unless it be that overlying the pink 

 sandstone just referred to. 



The accompanying (somewhat ideal) section of the island, chiefly along a line 

 running east from the boat-house on the bayou to Judge Avery's house, thence in 

 an east-northeast direction to Prospect HiU, and thence curving southward, exhibits 



GeolDgical Section, of Petite Anse laland, Xauisiana. 



the general geological structure, as deduced from my observations; the vertical 

 elevation being, of course, much exaggerated. Its location will be best understood 

 by referring to the map (see above). 



It will be seen that, starting from the stump stratum, No. 1, as a point of refer- 

 ence, the section of the strata on the western slope shows a general correspondence 

 to that of the southern portion of the Port Hudson bluff, where the clay stratum, 

 No. 4, may also be traced along the entire outcrop. 



BELLE ISLE AND ORANGE ISLAND. 



I will here briefly give the data I possess concerning the geology of these two 

 extreme members of the group of five. 



According to Thomassy, the uppermost strata at Belle Isle consist of "sands 

 similar to those of the Red River country" — perhaps a reddish loam similar to No. 

 7 of the Cote Blanche profile. Beneath lie others " identical with those of the 

 Sabine Hills" (whitish hardpan'?); finally, lower down we have a formation of 

 "calcaire grossier," "crumbled to pieces" — doubtless the crystalline calcareous 

 nodules seen at Cote Blanche, according to the description given me by others. 



