32 



preciable quantity. Such matter, there is reason to believe, would 

 not in general prove directly beneficial to the soil. The former has 

 been thought positively detrimental to vegetation, and certainly 

 when applied in considerable quantity, this is its effect What 

 agency it might exert in a more diluted state, and mingled with 

 other matter, we are without the means of determining. Probably 

 under such circumstances it might operate as a stimulant, and thus 

 contribute to the growth. The same doubts arc also applicable to 

 the other substance above named. Yet in some well authenticated 

 cases, the action of these copperas and sulphur clays has been found 

 strikingly beneficial. In these instances, however, it would seem 

 that much if not all the benefit was produced by the effectual protec- 

 tion which even minute quantities of these substances, especially the 

 latter, afford against the attacks of insects. In a cotton field in 

 which all the alternate rows were lightly sprinkled with earth of this 

 description, the plants so treated grew up vigorous and healthy, 

 while the others became sickly and were nearly devoured by insects. 

 Much careful observation is required to determine the kind and 

 mode of influence which these substances exert, and it would be 

 premature, in our present ignorance of the matter, to assert any con- 

 victions on the subject. The presence of the former of these ingre- 

 dients, if not recognised by the copperas flavour, will be readily dis- 

 covered by steeping the earth in water, decanting the clear liquid, 

 boiling it down to a small volume, and then adding tincture of galls 

 or prussiate of potash. A black or brown colour with the former, 

 or a blue one with the latter, would indicate its presence. The ex- 

 periment, however, should be made in a glass or china vessel. The 

 sulphur becomes manifest to the smell when the clay is heated, and 

 even at ordinary temperatures its peculiar odour may often be per- 

 ceived. 



The following table exhibits the per centage of carbonate of lime 

 in a number of the Miocene marls which I have examined. The 

 analysis were made with the " apparatus for analysing calcareous 

 marls and other carbonates," described in The Farmer's Register 

 and Journal of Science. No attempt was made to ascertain the pro- 

 portions of sand, clay or greensand, because the trouble of the ana- 

 lysis would have been increased more than ten fold, and probably no 

 useful result could have been attained. In each experiment the ap- 

 pearance and character of the undissolved matter was noted, and 

 thus a general estimate formed of the other ingredients of the speci- 



