566 



THE POPULAR SCIENCE MONTHLY. 



POPULAR MISCELLANY. 



Value of Soil Analysis. Professor E. 

 "W. Hilgard, in a paper in the "American 

 Journal of Science," on " The Objects and 

 Interpretation of Soil Analyses," accepts as 

 correct the principle that, other things be- 

 ing equal, productiveness is, or should be, 

 sensibly proportional to the amount of avail- 

 able plant-food within reach of the roots 

 during the period of the plant's develop- 

 ment, provided that such supply does not 

 exceed the maximum of that which the plant 

 can utilize, when the surplus simply remains 

 inert. For finding the exact value of the 

 soil from analysis, it is necessary, however, 

 not so much to find the actual amounts of 

 the constituents in the soil, as to find the 

 amounts which are accessible to and assimi- 

 lable by the plants. The problem is, then, 

 to find a solvent which shall as nearly as 

 possible represent the action of the plant 

 itself. Analyses of European soils fail be- 

 cause virgin soils do not exist in Europe, 

 and no generalizations can be drawn from 

 the examination of any spot. In the United 

 States we still have perfectly natural soils 

 in nearly every part of our territory, with 

 the original vegetation, which reveals so 

 much to the farmer, still growing upon 

 them. Professor Hilgard's method of anal- 

 ysis starts from the observation of the pro- 

 ductive qualities of the soil as indicated by 

 the native growth. He then tries to ascer- 

 tain what are the peculiarities of the soil 

 that favor this kind of growth, as distin- 

 guished from some other growth on some 

 other soil. As a rule, a soil showing a high 

 percentage of plant-food is fertile ; but the 

 converse is not always true ; a soil having 

 a low percentage is not necessarily poor. 

 A loose soil, by enlarging the sphere of ex- 

 pansion of the roots may enable them to 

 reach as large quantities of food, even when 

 it is more widely scattered, as they can find 

 in a more highly charged but more compact 

 and less penetrable soil. Hence mechan- 

 ical conditions should always be taken into 

 account. The analyses so far instituted 

 prove that, other things being equal, the 

 thriftiness or present productiveness of a 

 soil is measurably dependent on the pres- 

 ence of a certain minimum quantity of lime. 



The evidence on this point is " overwhelm- 

 ing." The lime operates by effecting the 

 more rapid transformation of vegetable mat- 

 ter into active humus, by retaining the 

 humus against the oxidizing influence of hot 

 climates ; by rendering minute percentages 

 of phosphoric acid and potash effective ; by 

 a tendency to secure the proper mainte- 

 nance of the conditions of nitrification ; and, 

 physically, by promoting the flocculation of 

 the soil. After that of lime, the proportion 

 of phosphoric acid seems to be the most im- 

 portant factor in the productiveness of soils. 

 A certain percentage of potash is required, 

 but it is present in most soils ; and Profess- 

 or Hilgard infers, generally, that " potash 

 manures are not among the first to be 

 sought for after the soils have become 

 'tired ' by exhaustive culture." Iron, in the 

 shape of ferric hydrate finely diffused, ap- 

 pears to be an importaut ingredient, valu- 

 able on account of its physical, and partly 

 also of its chemical qualities. It has a 

 high absorptive power for gases, and soils 

 in which it occurs resist drought better 

 than others ; and the universal preference 

 given by farmers to red lands shows the re- 

 sults of experience in this respect. The ef- 

 j ficiency of the hydrate depends essentially 

 upon a state of fine division; and when 

 merely incrusting the sand-grains, or aggre- 

 gated into bog-ore grains, it exerts little or 

 no influence, although the analysis may 

 show a high percentage. On the other hand, 

 ferruginous soils are the first liable to dam- 

 age from imperfect drainage, overflows, etc. 



The Eocene Strata of Alabama. Mr. 

 Angelo Heilprin has communicated to the 

 Academy of Natural Sciences of Philadel- 

 phia an effort to arrange the Eocene de- 

 posits of Alabama, determine their depth, 

 and fix their relative position in the geo- 

 logical system. For this purpose he has 

 given comparative reviews of the examina- 

 tions of various exposures, including the 

 Claiborne Bluff and sections on Bashia 

 Creek, Clarke County, and at points on the 

 Tombigbee River. The Claiborne Bluff was 

 formerly considered to be near the base of 

 the Eocene system, but it appears to be 

 underlaid by the strata which crop out at 

 other points, indicating a thickness of at 

 least 200 feet, if not more, of Eocene de- 



