TRANSACTIONS OF THE SECTIONS. 37 



Contributions to the History of the Magnesian Limestones. 

 By Mr. Richardson. 

 The author, considering the great importance of the magnesian limestones, both 

 to the manufacturer and agriculturist, conceived that an account of their composition 

 might prove acceptable. He examined the various limestones systematically, accord- 

 ing to the excellent arrangement of Prof. Sedgwick, and collected the results bf his 

 analyses in a tabular form. The insoluble residue of the specimens subjected to 

 analysis contained, in every case, organic matter. The analyses proved a very great 

 variation in the quantities of lime and magnesia. Mr. Richardson argued, that the 

 deposition of the lime and magnesia must have been effected simultaneously, from 

 the fact of layers of limestone existing above and below the magnesian limestones, in 

 which layers no magnesia can be detected. He was inclined to ascribe their depo- 

 sition to the influx of waters holding chloride of magnesium in solution, which, 

 meeting with calcareous matter held in solution by an excess of carbonic acid, robbed 

 it of that excess, and the two carbonates of lime and magnesia fell together. 



On the Agricultural Importance of ascertaining the minute portions of matter 

 derived from Organic Sources that may be preserved in the Surface Soil, 

 and on the Chemical means by tohich its presence may be detected. By 

 Dr. Daubeny. 



The researches of Sprengel and Liebig, by showing the manner in which minute 

 quantities of certain ingredients may impart to the soil into which they enter as 

 constituents entirely new properties with reference to the purposes of agriculture, 

 have given additional interest to the methods of analysis, which aim at determining 

 the chemical composition of the surface, and of the substratum from which the 

 former principally derives its chief ingredients. The rude mechanical method adopted, 

 even by such chemists as Sir H. Davy, is no longer considered sufficient. The 

 nature, as well as the amount of the organic matter present, and the existence 

 of phosphates, &c. in the proportion of ' , or even _L th part of the en- 

 tire mass, are points deserving investigation, and afford a clue to the description 

 of manures most likely to be useful, and to the general treatment which the 

 land may require. It is also obvious, that the same importance attaches to a 

 knowledge of the constitution of the subsoil, since the advantages of exposing to 

 atmospheric influences, and thus disintegrating, the portions underneath, by deep 

 ploughing, and other methods of bringing the subsoil to the surface, will in a great 

 degree depend upon its containing ingredients which the crop requires for its sub- 

 sistence, and of which the superficial soil has been already in a great degree 

 exhausted. Thus, for example, it will often become a question with the farmer, 

 whether it be more economical to mix with the soil a given quantity of phosphate 

 of lime, or to incur the labour of so breaking up a portion of the subjacent rock, as 

 to unlock, as it were, for the use of the crop, that quantity which it contains in 

 close union with its other constituents. This inquiry, however, presupposes a 

 knowledge on his part of the existence of phosphate of lime in the soil, and of the 

 relative proportion it bears to the other ingredients ; data which can only be obtained 

 through the assistance of refined chemical analysis. A few simple and easy calcu- 

 lations may show how very small a proportion of this ingredient might suffice during 

 a long period of time, for the demands even of those crops which require the largest 

 amount of it for their nutrition. Suppose the subsoil of a single acre of ground, 

 turned up to the depth of a foot, to weigh 1000 tons : now if this rock should be 

 found to contain only yoWth part of phosphate of lime, it will follow that no 

 less than a ton of this substance might be extracted from the uppermost foot of the 

 subjacent rock, by the action of the elements, or by chemical means. Now one 

 ton of phosphate of lime would be adequate to supply 125 tons of wheat, or 680 

 tons of turnips. And if we reckon the average crop obtained from an acre of land 

 to be, of wheat, one ton, and of turnips, fifteen, it is evident that we have at hand 

 as much phosphate of lime as would be necessary for 125 crops of the former, or 

 forty-five crops of the latter. Dr. Daubeny said he had great reason to believe, that 

 many of our secondary rocks, those especially which contain organic remains, and 

 which appear in a great measure to be made up of shells, would be found, if ex- 



