44 AMERICAN AGRICULTURE. 



and Ireland. It is also found on the coast of France, and 

 particularly in Brittany, where it is known by the name of 

 trez. This produces prodigious effects on peaty, clay and 

 other soils, to which it is applied at the rate of 10 to 15 tons 

 per acre. It is so much esteemed for the former, that it is 

 sometimes carried to a distance of 100 miles. It is proba- 

 ble, there are similar deposits on the coast of some of the At- 

 lantic States, though I am not aware of its application for 

 agricultural objects. Its great value as a top dressing, will 

 fully justify exploration, for the purpose of detecting it 

 wherever it may exist. 



GREEN SAND MARL. 



There are extensive beds of a green sand, (generally 

 though improperly termed marl), which run through a sec- 

 tion of New Jersey, from which farmers have derived an 

 astonishing addition to their crops. Much of it is found by 

 analysis, to contain scarcely an appreciable quantity of 

 lime, but it readily yields a large amount of potash, varying 

 from six to 15 per cent. From a careful analysis of eight 

 different specimens, Professor Rodgers found in it an aver- 

 age of 10 per cent, of potassa. The effect of this applied 

 to the barren sands, which abound in that neighborhood, 

 has been so favorable, that lands which before could be 

 bought for three dollars per acre, would afterwards bring $40. 

 Several deposits of green sand in the counties of Plymouth 

 and Barnstable, Mass., similar in external appearance to the 

 foregoing, were explored by Professor Hitchcock, and speci- 

 mens were analyzed by Dr. Dana, without, however, de- 

 tecting any" qualities of decided advantage to agriculture. 



GYPSUM PLASTER OF PARIS OR SULPHATE OF LIME. 



This is a combination of lime with sulphuric acid and water, 

 in the proportion of 28 of lime, 40 of acid, and 18 of water. 

 It is frequently found in connection with carbonate of lime, 

 clay, &c. The use of gypsum has been attended with great 

 benefit in most parts of the United States ; and by many 

 of the most experienced farmers in certain localities, it is 

 justly considered as indispensable to good farming. Like 

 other saline, and indeed all manures, it acts beneficially only 

 on soils which are naturally dry, or have been made so by 

 artificial drainage. It is felt most on sands and loams ; but 

 generally, it is advantageously added to clay soils, requiring 

 more for the latter, and for all such as contain a large pro- 



