Mississippian and Caddo Culture Ceramics
The generally accepted dates for this type of ceramics are from 800-1600 CE.  Around 1700 the production of this ware by native peoples declined due to European migration and influence into the area.  Mississippian as well as Caddo ceramics are unique in that the production methods use what is called shell tempering to lower the rate of the workable clay paste.  Clay from the river beds of the production region has a high organic content that burns of when fired causing problems with uneven shrinkage when drying as well as being fired.  This technique used shell fish, specifically muscles, from rivers as a form of grog to reduce shrinkage.  Sand was also used as well as ground up bisque material in the clay mixture for the same purpose.  The shell material was ground up and wedged into the clay body during the wet state.  Some examples of this type display a very large particle size and can clearly be seen in the clay after firing.  After firing the vessels made would also withstand the thermal shock associated with cooking over an open fire. 
Great Serpent Mound

Great Serpent Mound. Ohio. c. AD 1070.
Stokstad, Marilyn. Art History. Revised Second ed. Vol. 2. New York: Prentice Hall Inc., and Harry N. Abrams Inc., 2005

Cahokia. Mississippian culture. AD 1200.
Penney, David W. North American Indian Art. New York: Thames and Hudson, 2004.