120 THE ECONOMIC EESOUKCES OF ST. MARY's COUNTY 



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 northwestern portion 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 

 latter is the principal use to which it is put. It has been thought that 

 the diatomaceous earth might be of use in certain branches of pottery 

 inanufacture, which require on the part of the materials refractoriness 

 and an absence of color wlien burned. Dr. Ileinrich Ries tested a sample 

 of the diatomaceous earth from Lyons Creek at cone 27 in the Deville 

 furnace and found that the material fused to a drop of brownish glass. 

 The non-refractory character of the diatomaceous earth is thus clearly 

 demonstrated. It is also used in the manufacture of fire and heat- 

 retarding cements and fire-proof building materials, such as solid brick 

 and hollow brick for partition walls and floors. 



