CALCAREOUS MARL. 255 



An analysis of the clays owned by the Jamestown Portland Cement 

 Corporation, and which outcrop on the York Elver, is reported by 

 Mr. Brown as follows : 



Analysis of clay from the Jamestown Portland Cement Corporation's 

 property, Yorhtown, Va. 



Silica (SiO.) 65.94 



Alumina (ALO3) 22.50 



Ferric oxide ( FeA) 6 . 60 



Lime (CaO) 1.23 



Magnesia (MgO) 1.50 



A laboratory Portland cement plant owned by the American Cement 

 Engineering Company was erected on the property of the Jamestown 

 Portland Cement Corporation at Yorktown, for demonstrating purposes, 

 in order to manufacture in the ordinary way, and according to mill methods, 

 the marls and clays into standard Portland cement. The raw materials 

 for this plant were secured from many different openings made in the 

 marl deposits, and represent average samples such as will be secured in 

 the operation of steam shovels when the marls are taken from bottom to 

 top of the deposit. 



Portland cement was successfully made from the marls occurring at 

 Yorktown, which judging from the results of tests made in a number of 

 the Government and private consulting testing laboratories, is in every 

 respect the equal of many of the standard brands of Portland cement of 

 wide reputation. 



The Colonial Portland Cement Corporation's property is located at 

 Grove, Virginia, on the James Eiver and about half a mile from the 

 Chesapeake & Ohio Railway. Two marl beds occur designated as "upper" 

 and "lower," separated by an average thickness of 9 feet of clay, the top 

 of which marks the bottom of the "upper" marl. The beds are exposed 

 in a line of bluffs along the north side of James River, and in ravines which 

 have cut down to a depth of from 20 to 30 feet. Plate XIX, figure 2, 

 is a view of the marl beds exposed in the bluff along the river. 



From measurements made in test pits and in natural exposures, the 

 "upper" marl bed shows an average thickness of not less than 12 feet, 

 and in many places it is 30 feet thick. The "lower" marl bed lies im- 

 mediately below the clay bed and has been exposed to a depth of 10 feet, 

 with the bottom of the bed not reached. The marl and clay beds are of 

 Miocene- age and belong to the Yorktown formation. 



