CEMENT MATERIALS. 71 
Biloxi. When used alone the clay is too dark for making a fine grade of ware. It is there- 
fore mixed with a clay from Iuka, Miss., and the combination produces a lighter colored 
ware which has gained an enviable reputation. 
QUATERNARY CLAYS OF THE YAZOO DELTA. 
Only the more arenaceous and gumbo clays are found in the west-central section of the 
tte. Over a large portion of the Yazoo delta there is a thin veneering of fine sand or silt 
■iich has been deposited during successive overflows of Mississippi River and the other 
ams throughout the area. The sands and silts occur only along the banks of the present 
or ancient streams. The delta streams carry a large amount of suspended material and 
when they overflow the greater portion of the sediment is dropped near them. The banks 
of the streams are thus built up higher than the interstream areas. This is true of all the 
streams of any size throughout the country subject to overflow. The width of the super- 
added deposits extending back from the streams depends on the size of the streams. 
The material occupying the surface of the interstream areas is a tough gray aluminous 
clay commonly known as "buckshot clay," though it does not always contain the small 
iron pebbles which have given rise to the name. When wet the clay forms a sticky mass 
which is a great hindrance to wagoners. It is, nevertheless, easily cultivated and pul- 
verizes into a loose fertile soil well adapted to cotton and corn. 
It has been estimated that this clay comprises 65 per cent or more of the soils of the delta. 
The relation of the silty loam to this gray gumbo clay is shown in the following section at 
Clarksdale, Coahoma County: 
Section at Clarksdale brick plant. 
Ft. In. 
4. Black humus soil 10-12 
3. Light-gray sandy clay containing small flecks of mica 3 
2. Fine gray siliceous sand, with irregular layers of sandy clay 3 
1. Gray, stiff "buckshot clay" 2 
The upper 6 feet of sands and clays are united as they come from the pit, and the combined 
mass is used for making brick. The lowest clay member is considered too compact for 
making brick; it requires too much time for drying and the bricks check before drying. 
One-half mile west of Clarksdale is an abandoned river channel about 1 mile in width. 
It is now filled up until it is but 10 to 15 feet lower than the level of Clarksdale. ■ West of 
the old channel the tough gumbo clay, which is 6 feet below the surface at Clarksdale, under- 
lies about 12 to 15 inches of humus soil. This clay has been used, after burning, as a road 
material, and as such will be discussed later (p. 86). 
CEMENT MATERIALS. 
By Edwin C. Eckel. 
PORTLAND CEMENT. 
The important building material known as Portland cement was first manufactured in 
England in 1824. Its name is not, as is commonly supposed, due to the fact that it is manu- 
factured at Portland, England, Portland, Me., or Portland, Oreg., for it is not and never 
has been made at these points. The name "Portland" was applied to this cement because, 
after setting, it resembles somewhat a gray limestone extensively quarried at Portland, 
England. The original patents on Portland cement have long since expired, and it may 
now be manufactured at any point where suitable raw materials and fuels are obtainable, 
and where a good market exists for the finished product. 
Portland cement was first manufactured in the United States about 1875. Until 1890 
the American industry showed little progress, but since that date its marvelous growth has 
created a widespread interest in the raw materials and in the methods of manufacture. This 
interest is not confined to those who have a direct financial stake in the industry, as the 
product is so widely used and its uses are so rapidly increasing that some knowledge of its 
manufacture and properties is of advantage to everyone connected, directly or indirectly, 
with engineering or building operations. In its importance to our present civilization 
