112 NORTH-CAROLINA GEOLOGICAL SURVEY. 



compost heap containing a hundred bushels of marl be form- 

 ed, mixing leaves or any organic matter as stable manure, 

 and then add three bushels of quick lime to the mass, and 

 incorporate the ingredients together by shoveling them over 

 twice. Gypsurn will be formed by combining with the sul- 

 phuric acid in combination with the iron. The compost is all 

 the better for the lime, though it is possible the gypsum may 

 not in all instances prove itself useful. Astringent marls, 

 when in heaps in the open air, lose their copperas and other 

 soluble salts by solution in rain water to which they are neces- 

 sarily exposed, they undergo a leaching process by which 

 they are freed of their injurious properties. Another method 

 may be resorted to when it is found that vegetation is being 

 injured, or has been by the experience during the year of its 

 application, to plough deep and mix the marl with a large 

 quantity of soil ; the fertility will be restored. It is by no 

 means difficult for any farmer to test his marl prior to its use 

 if he wishes to ascertain whether this astringent salt is pre- 

 sent. To do this, let the marl be boiled in rain water ; strain 

 it, or let the turbidness of the solution disappear by rest; 

 pour off the clear liquid, and if sulphate of iron and alumina 

 is present, it will turn black by adding a solution of strong 

 tea to it ; it will become a dirty white by lime water and a 

 solution of the leaves of red cabbage change it to red, show- 

 ing the presence of an acid salt. Most of the marls of the 

 State contain these salts. Where they are abundant unde- 

 composed pyrities will be found in masses adhering to por- 

 tions of petrified wood or inseparate concretions in the marl. 



84. Writers upon the efficacy of marl as a fertilizer, have 

 entertained different opinions. As the progress of agricul- 

 ture has been promoted, and observation and experiments 

 multiplied upon the effects of different bodies upon vegeta- 

 tion, these opinions have become more consistent and reliable. 



Some writers have maintained that lime alone is the effec- 

 tive agent; others that it is pyrites, or else is due to the 

 presence of animal matter, which has been derived from the 

 fossils of the beds ; others, still, to the presence of phosphate 



