Xlvi REPORT OF THE STATE GEOLOGIST. 



GLAUCONITIO BEDS. 



Directly below the black clays on the northeast, and what is sup- 

 posed to be the continuation of the Sabine Eiver Beds on the south- 

 west, there is a deposit of sands with clay, and a considerable amount 

 of glauconite or greensand. The fossil shells found in it, in great 

 numbers, are identical in species with many of those found in the 

 greensand marls of New Jersey, and prove its close relationship to 

 those in time or conditions of deposition. The admixture of sand and 

 greensand with the clays of this belt, which is narrow in Northeast 

 Texas (and of entirely unknown extent in the southwest), makes its 

 resulting soil less sticky, and therefore more easily worked than the 

 Main Black Prairie, which it so closely resembles in color and fertility. 

 It must therefore be of necessity a most excellent fruit region. 



THE PONDEROSA MARLS. 



This great body of clay, which is the immediate source of that fer- 

 tile soil so well known as the Black Waxy Prairie, has a thickness of 

 some twelve hundred feet. These clays lie directly below the sandy 

 strata of the Grlauconite Beds on the east, and rest on the gently slop- 

 ing beds of the Austin Chalk, the outcrop of which marks their west- 

 ern boundary, giving us an area thousands of square miles in extent, 

 which is one of the grandest agricultural countries of which we have 

 any knowledge. They are originally of a light blue color, due to the 

 iron they contain being combined with its minimum amount of oxy- 

 gen, and seem to be very massive, but the action of atmospheric agen- 

 cies brings out their laminated structure and gradually alters their 

 color to yellow, by the combination of the iron with more oxygen, 

 forming the peroxide (which is equivalent to iron rust); and finally, 

 when the iron and limy material are acted upon by vegetation, it gives 

 it the deep black color so characteristic of the soil. 



The principal fossil found in these clays is a very heavy oyster, 

 from which the clays receive their name. Toward the top, as the 

 Grlauconite Beds are neared, the clays become more fossiliferous, and 

 many shells resembling those of the overyling beds are found. The 

 great value of the Ponderosa Clay is in its superior soil, the elements of 

 which are due to the material derived from the wearing away of por- 

 tions of some of the older formations to the north and west, and their 

 redeposition in their present localities. These consist of clays, lime, 



