130 THE ECONOMIC RESOURCES OF CALVERT COUNTY 



mixed with so much sand that the lime forms only a small percentage, 

 but in other places the amount of lime exceeds 90 per cent. 



The value of the shell marls and methods for using them are thor- 

 oughl}? discussed by Professor H. J. Patterson in a Bulletin of the 

 Maryland Agricultural Experiment Station (Ko. 66, May, 1900). He 

 states that the lime has an especially beneficial effect upon sandy soils, 

 such as prevail throughout Calvert County, in improving their physical 

 characteristics. This it does through its cementing action which ren- 

 ders such soils less porous and thus enables them to retain moisture 

 better. Chemically, lime corrects the acidity of the soils through its 

 neutralizing effect upon acids, acting upon other soil constituents, ren- 

 dering them available for plant food, and finally serves as a plant food 

 itself. Many experiments which have been tried in various places all 

 show the value of lime as a fertilizer, and experiments in this State show 

 that better results were obtained by the use of shell marl than with 

 burned-stone lime. No doubt, any of the soils of Calvert County might 

 be considerably improved at small expense by the generous use of shell 

 marl, deposits of which are readily accessible to a large part of the 

 county. 



THE DIATOMACEOUS EARTH. 



Diatomaceous earth, infusorial earth, or tripoli is a siliceous deposit 

 composed mainly of the microscopic tests of diatoms, a low order of 

 aquatic plants. The material is soft, porous, light in weight, and very 

 friable. When fresh it is greenish in color but on exposure to the air 

 the color changes to buff or almost pure white. The diatomaceous earth 

 occurs in the lower part of the Calvert formation and is well exposed in 

 many places along the Bay and river shores and in the tributary stream 

 valleys in the northern half of the county. 



The diatomaceous earth, on account of its porosity and compactness, 

 is used in water filters. It is reduced readily to a fine powder and makes 

 an excellent base for polishing powders. On account of its porous 

 nature, diatomaceous earth is used as an absorbent in the manufacture 

 of dynamite, while its non-conductivity of heat makes it a valuable in- 

 gredient in packing for steam boilers and pipes, and in safes. This 



