100 MASSACHUSETTS AGRICULTUEE. 



average length from north to south of seventy miles and a 

 breadth of fifty miles. It is in the nature of a deposit varying 

 from six inches to two or three feet in thickness, and spread 

 over this whole area of many hundred square miles, in some 

 places appearing at the surface, but usually several feet below, 

 and yielding from 1,000 to 1,500 tons per acre in amount. 

 Instead of being in a bed sloping to the sea as the river falls, 

 about six feet to the mile, it is found in " steps" of diiferent 

 elevations. The chief part does not consist in fossil-bones, 

 but rather in nodules or conglomerates. These are generally 

 rough and irregular in form, water-worn and rounded, per- 

 forated by boring-shells, cavernous and fossiliferous, though 

 generally only casts remain, the original carbonate of lime of 

 the shelly portions having been removed by solution, leaving 

 only its trace or impression, as in a mould, in the phosphatic 

 mud in which it seems to have been buried. Suppose a layer 

 of rock, such as I have described, piled evenly on a floor 

 twelve or eighteen inches thick like cobble-stones on a paved 

 street, scatter among them indiscriminately bones of marine 

 and terrestrial animals, let a soft paste of clay and sand be 

 poured on until all the interstices are filled, cover this with a 

 foot or more of soil, and a good idea of this wonderful bed 

 will be formed. 



"«^IAT IT IS. 



Without doubt it is purely animal in its origin. The bones 

 and teeth are, of course, unmistakable, and the nodules con- 

 tain, as shown by abundant analyses, an average of from 57 

 to 67 per cent, of true hone pJiosphate of lime, and under the 

 microscope they exhibit unmistakable characters of bone. 

 They are easily soluble even in dilute acids, and being almost 

 free from phosphate of iron and alumina, with a very low per- 

 centage of carbonate of lime, this material stands among man- 

 ufacturers superior to any other supply in the world. The 

 irregular, uncertain and deeply-buried deposit of " coprolites " 

 of the London basin is the nearest known approximate to 

 this. This, hoAvever, contains generally far less carbonate 

 and more phosphate of lime, and is, proportionally, more 

 valuable. The coprolites are also hard, deeply-buried, and 

 very scattered and uncertain in their location. These bones, 

 especially those of now extinct animals, retain in a great meas- 



