EXPERIMENT STATION BULLETINS. 



497 



it lies beneath several feet of it. The thickness of the beds or deposits 

 is also quite variable. The marl owes its existence to lime that was 

 washed out of the surrounding soil nad deposited in lakes and to the 

 accumulation of shells of lower animals such ns the mollusca. 



As it occurs in the beds, marl is generally a past}^ mass varying in 

 color from light to dark-gray depending upon the iiupurities present. 

 Upon di-jing it becomes lighter in color and is easily crumbled, or 

 broken up. If a small amount is placed in half a tumbler of strong 

 vinegar or weakened muriatic acid it will give oif bubbles of gas and 

 go into solution. Tliis is one method ol" ith'utifying niarl as well as 

 roughly estimating its 'purity. !So)ae deposits are tilled with small 

 shells which aid in identifying this material. 



Figure 2. An Kiisilj- AcccssiMi- Marl Bed. 

 A more general iililizulion of Michigan's marl deposits for agricultural purposes is desirable. 



Water Content atul WeigJtt of Marl. When marl is thrown out of the 

 bed and allowed to drain tlie amount of moisture retained is quite 

 variable and depends somewhat on the amount of impurities. In general 

 the purer the marl the less water it will hold but sandy marls contain 

 less water than clay marls. Tlie following table sliows the water con- 

 tent, the weight of a cubic yard and the weight of lime carbonate con- 

 tained in a cubic yard of several ^Michigan marJs. 



