Lake Pontchartrain, Louisiana, originated from the Gulf of Mexico by a delta finger of the Mississippi River uniting with the mainland and enclosing a part of the gulf between the finger and the mainland. After its isolation, connection was and is still maintained between the lake and the gulf through tidal channels.

It originated from a mixed continental and marine environment and is slowly passing into a continental environment with corresponding changes in its medium from marine to brackish to fresh water. Inasmuch as the environmental changes have not been progressively uniform at all times and at all places, there are marked variations in the character and distribution of the sediments and the associated life.

In general, wave action, littoral currents, and inflowing streams are the controlling factors in the textural distribution of the sediments, which are coarse along the outer margin where water activity is greatest and fine in the deep and quiet waters of the lake. Bottom topography does not exert as important an influence as the foregoing factors in the textural distribution of the sediments.

Aside from anomalies, the organic content is high where the texture is fine, and low where the texture is coarse. The organic matter of the lake seems to be principally vegetable in origin.

The arrangement of the sediments of Lake Pontchartrain into distinct beds, the regularity in areal as well as vertical distribution, and the compacting of material increase with depth.