REPORT OF THE STATE GEOLOGIST. xlvii 



Texas is abundantly supplied witb this material. Not only does it 

 occur in immense deposits in the Permian Beds west of the Abilene- 

 Wichita country, but all through the Timber Belt Beds it is found 

 along the streams and scattered through the clays as crystals of clear 

 selenite, often miscalled "mica" or "isinglass." It is of all degrees of 

 purity, from the pure selenite to an impure gypseous clay. So far it has 

 been little used for this purpose in Texas. 



GREENSAND MARL. 



This marl is a mixture of sand and clay with greensand, and often 

 contains quantities of shells. Greensand, or glauconite as it is often 

 called, is a mineral of green color composed of silica (sand) in chemical 

 combination with iron and potash, and usually contains variable quan- 

 tities of other substances. This marl also contains more or less phos- 

 phoric acid, and the shells furnish lime. Where it occurs in its original 

 and unaltered condition it is of a more or less pronounced green color, 

 due to the color of the greensand in it. Where it has been subjected 

 to chemical action the greensand is gradually decomposed and the 

 iron unites and forms hydrous oxide of iron, or iron rust. This altera- 

 tion gives rise to a great variety of color in the different beds of the 

 material. When it is fully altered in this way it forms the red or yel- 

 low sandstone so much used in East Texas. 



Numerous analyses have been made of these marls, both in their 

 original and altered conditions. They contain, in all the samples tested 

 at least, lime, potash, and phosphoric acid, just the elements that are 

 required to fertilize the sandy soils and to renew and increase the fer- 

 tility of those that have been worn out. These^ elements occur in the 

 marl in variable amounts, and less in the altered than in the unaltered 

 material. In nearly every instance, however, the amounts were suffi- 

 cient to be of great agricultural value to every field within hauling dis- 

 tance of such a deposit. It often happens, too, that these beds of marl 

 lie in closest proximity to the very soils on which they are most needed, 

 and all the farmer has to do to secure the desired results is to apply it 

 as a fertilizer. 



If any proof is wanted of the adaptability of these marls, and of their 

 great value on just this character of soil, it is shown in New Jersey, 

 where exactly similar conditions exist. In that State there were large 

 areas of pine land soils which were, like ours, of little agricultural value 

 because of the small amounts of potash, phosphoric acid, and lime con- 



