472 GEOLOGY OF NORTHWESTERN TEXAS. 



elements soils often contain other ingredients which are, when in excess, 

 quite deleterious to plant life. 



These elements are contained in the primitive or granitic and metamorphic 

 rocks, with little or no admixture of the elements or combinations caused by 

 the admixture of the acids with the basic elements. As there are no primi- 

 tive or metamorphic rocks in that part of the State to which this Report re- 

 lates it will be unnecessary to discuss the question of the mode of occurrence 

 and the combination of these elements in the primitive rocks. The soils of 

 this part of the State are derived from the sandstones, limestones, and clay 

 and shale beds found in the district. 



These stones and beds were originally formed by the disintegration of the 

 material of the primitive rocks. The materials of the limestone were brought 

 down by the rivers into the sea, and were finally deposited with the com- 

 minuted shells of the ocean in the deep, quiet ocean in beds as they are now 

 formed. These limestones are composed principally of calcium, carbon, and 

 magnesium, with iron, silica, clay, bitumen, and other substances as impurities. 



The sandstones were deposited along the sea beach, and are composed prin- 

 cipally of silica, being nothing more than fragments of quartz. This material 

 is bound together by clay or lime, and sometimes by iron. 



The clay beds were formed in the shallow seas and along the estuaries and 

 mouths of rivers, and are principally aluminum silicate and carbonate of lime. 



Soils are largely indebted to vegetable life for their fertility and for their 

 ability to receive heat and moisture and to transmit it to the growing crops. 

 This vegetable material after it has reached a certain state of decay is called 

 humus. ' This material has no fixed chemical constituents, owing to the effect 

 produced and the combination formed with other substances in the process 

 of decay. Many soils own their dark color to this material. It renders a 

 soil more susceptible to heat and moisture. It also causes the undissolved 

 particles of rock material remaining in the soil to disintegrate and give up 

 their unused material to form a part of the soil. 



All soils of whatever kind and for whatever agricultural purposes they are 

 used must be placed in proper condition to sustain the intended plant The 

 plant is dependent upon the soil for a place in which to grow and mature. 

 It must have food, air, heat, and moisture; and if either of these are lacking 

 the plant withers away before maturity, even if it germinates or begins to 

 grow. 



The first important thing in regard to the soil is that it shall be of sufficient 

 depth to support the plant in its upright position while growing. If there be 

 no depth of earth the roots can not penetrate deep enough to hold the plant 

 in position. The roots of a plant are not only for taking up nourishment 

 from the soil, but also for the purpose of bracing and supporting the plant in 



