DISEASED CROPS CAUSED BY MARLING. 157 



raised in 1830, by adding gypseous earth, and which was succeeded 

 by a good growth of corn, free from every mark of disease, in 1832. 



5th. A good dressing of putrescent manure removes the disease 

 completely (see Exp. 11, 12, 13). All kinds of marl (or fossil 

 shells) have sometimes been injurious ; but such effects have been 

 more generally experienced from the dry yellow'marl, than from 

 the blue and wet. 



The inferences to be drawn from these facts are obvious. They 

 direct us to avoid injury by applying marl lightly at first, and to be 

 still more cautious according to the existence of the circumstances 

 stated as increasing the tendency of marl to do harm. Next, if 

 the over-dose has already been given, we should forbid grazing 

 entirely, and furnish putrescent manure as far as possible ; or omit 

 one or two grain crops, so as to allow more vegetable matter to be 

 fixed in the land apply putrescent manures and sow clover as 

 soon as circumstances permit. One or more of these remedies 

 have been used on most of my too heavily marled land ; and with 

 considerable, though not always with entire success, because the 

 means for the cure could not always be furnished at once in suffi- 

 cient abundance. Other persons, who permitted close grazing, and 

 adopted a more scourging rotation of crops, have suffered more 

 damage, from much lighter dressings of marl than those of mine 

 which were injurious. 



But though the unlooked-for damage sustained from this cause 

 produced much loss and disappointment, and has greatly retarded 

 the progress of my improvements, it did not suspend my marling, 

 nor abate my estimate of the value of the manure. If a cover of 

 500 or 600 bushels was so strong as to injure land of certain 

 qualities, it seemed to be a fair deduction, that the benefit expected 

 from so heavy a dressing, might have been obtained from half the 

 quantity; if not on the first crop, at least on every one after- 

 wards. That surely is nothing to be lamented. It also afforded 

 some consolation for the evil' of the too heavy marlings already 

 applied, that the soil was thereby fitted to seize upon and retain a 

 greater quantity of vegetable matter, and would thereby ultimately 

 reach a higher grade of fertility. 



The cause of this disease is less apparent than its remedies. It 

 is certain that it is not produced merely by the quantity of calca- 

 reous earth in the soil. If it were so, similar effects, shown in 

 diseased crops, would always be found on soils containing far 

 greater proportions of that earth. These injurious effects have not 

 been known, to any extent, except on soils formerly acid, and made 

 calcareous artificially ; and not on neither neutral or calcareous 

 soils, even by the addition of a great excess of marl. The small 

 spots of land that nature has made excessively calcareous, by marl 

 beds cropping out at the surface of cultivated fields (as the speci- 



