252 PHYSIOGRAPHY AND GEOLOGY OF THE COASTAL PLAIN PROVINCE. 



they decompose, while the gastropod shell marls are much better on account 

 of their more friable texture and more rapid decomposition. The Chama 

 marls are especially desirable. Shell marl has been dug in past years at 

 numerous places in the A^irginia Coastal Plain, and used extensively 

 on the land, but little has been dug in recent years. 



Use in Portland cement manufacture. — Only within the past several 

 years has serious attention been drawn to the shell (calcareous) marls of 

 the Coastal Plain as raw material for use in mixing in the manufacture of 

 Portland cement. Investigations conducted by the State Geological Survey 

 show that extensive deposits of shell marls of good grade and suitable 

 for the making of Portland cement occur in many places in the Vir- 

 ginia Coastal Plain. The most favorable deposits are of Miocene age, the 

 areal distribution of which is shown on the accompanying map, Plate I. 

 Of the Miocene formations, the Yorktown is one of the most fossiliferous 

 represented in the series of Atlantic Coastal sediments. It has a thickness 

 in Virginia of approximately 125 feet and contains a very rich and varied 

 fauna. The formation outcrops in Gloucester, James City, York, Warwick, 

 Isle of Wight, and Nansemond counties. 



In tlieir natural state, some of the marls contain too large a percentage 

 of sand to be used directly in cement making, but must be treated by a 

 simple process before mixing in order to reduce the sand content, which 

 proportionately increases the calcareous matter. Associated with the marls 

 in many places are beds of clay of sufficient thickness and quality as to 

 render them suitable to mix with the calcareous marl for Portland cement 

 manufacture. 



Eecently, three plants of large capacity have been granted charters for 

 the manufacture of Portland cement in the Coastal Plain (Tidewater) 

 region of Virginia. These are the Norfolk Portland Cement Corporation's 

 plant located near Norfolk, the Jamestown Portland Cement Corporation's 

 plant to be located at Yorktown, and the Colonial Portland Cement Cor- 

 poration's plant to be located at the Grove, 7 miles east of Williamsburg. 

 Of these, the plant of the Norfolk Portland Cement Corporation has been 

 completed and is producing. The raw materials to be used by these plants 

 in the manufacture of Portland cement are the Miocene marls and clays 

 of the immediate area. 



The Norfolk Portland Cement Corporation's plant* located on the 

 southern branch of the Elizabeth Eiver opposite the United States Navy- 



wSummarized from an article by Wm. H. Stone in the Manufacturers Record, 

 Oct. 13. 1910, pp. 49-50. 



