CALCAREOUS MARL. 251 



degree, yet any excess of soluble acid in the soil would be highly detri- 

 mental. While most of our cultivated crops seem to need a slight acidity, 

 it is probable that tliey have the ability to create this condition to a 

 sufficient degree through the medium of the solutions sent out by their 

 roots. This being the case, it would seem that the aim should be to keep 

 soils in a neutral or slightly alkaline condition, so as to favor the growth 

 of root tubercles of the legumens and the desirable soil ferments. Liming 

 is excellent for correcting any excess of acidity, and is probably the most 

 effective and economical substance for bringing about these other desirable 

 conditions." It is a well-recognized fact that sheep-sorrel thrives in an 

 acid soil where grass and grain will scarcely grow at all. In such places 

 the application of lime or marl destroys the soil acidity with the resultant 

 destruction of the sheep-sorrel and renders possible the growth of profitable 

 crops. 



"The many chemical changes brought about by the action of lime on 

 soils result in producing physical changes which give soils new mechanical 

 characteristics. Lime has the power of changing the physical properties 

 of a clay soil and making it more friable and easily cultivated, and putting 

 it in a condition so that water may pass more freely through it. This will 

 make it less susceptible to extremes of dry and wet weather, and make it 

 a good home for the roots of the plants. The action of lime on sandy 

 soils may be said to be the reverse of that on clay soils; that is it has a 

 cementing action, making such soils stick together in such a condition 

 that they will hold more water and not dry out so rapidly." 



Shell marl is somewhat less valuable than commercial lime, because 

 of its slower action, yet all the advantages claimed for lime as a fertilizer 

 may be equally well claimed for the natural marl. In many places through- 

 out Tidewater Virginia shell marl has been extensively used and, except 

 when put on in too large quantities, has materially increased soil fertility 

 and proved a valuable stimulus to plant growth. In many places, however, 

 since the Civil War very little marl has been used, notwithstanding the 

 fact that much excellent marl is locally available. In some places the 

 fossil shells have been burned for lime, which is spread over the surface. 

 In this form the lime becomes effective almost immediately, which is 

 often very desirable. Where the shells are very well preserved and compact, 

 the action of the natural shell marl is very slow, some shells remaining in 

 the soils for a great many years almost unchanged. 



Generally the marls made up of the shells of Ostrea, Pecten, Venus, 

 and Crassatellites are poor fertilizers on account of the slowness with which 



