66 ECONOMICAL MINERALOGY. 



A very imperfect idea of the quantity of gypsum which exists in this State, will be obtained 

 from the account of it which has now been given. Even if we had the means of ascertaining 

 exactly the luiinber of tons at present annually raised, which I think cannot be less than fifty 

 thousand, it should be borne in mind that regular explorations are seldom undertaken ; and 

 that the amount, whatever it may be, is mainly the result of accidental discovery, and of oc- 

 casional labour by the farmer during the intervals of his other avocations. Immense beds 

 still lie unopened, which will at some future day yield their treasures. Perhaps one reason 

 why greater attention has not been paid to the enormous deposits of gypsum and marl which 

 exist in the western part of the State is, that the soil is naturally so fertile as seldom to re- 

 quire the employment of those artificial means of renovation which in most other countries 

 are necessary to the success of the agriculturalist. Still it camiot be doubted that in many 

 situations even here, much advantage would be derived from the use of these efficient fer- 

 tilizers. Lime, marl and gypsum, all of which can be so easily and so abundantly obtained 

 in many parts of our State, have almost entirely changed the agricultural character of New- 

 Jersey and Pennsylvania. With us, however, their great value does not yet appear to be duly 

 appreciated. 



It may not be out of place here to offer a few suggestions in regard to the origin of gypsum. 



From the uniformly regular appearance which the beds of gypsum present throughout the 

 western counties, the similarity in their geological associations, and the apparent heaving'up 

 of the strata which enclose them, it has been thought that they are the result of agencies now 

 in operation. The opinion indeed prevails quite generally among the inhabitants of the dis- 

 tricts where plaster beds are of most frequent occurrence, that they increase from year to year, 

 and that it is unsafe to commence important structures in situations where they are supposed 

 to exist. 



It seems not improbable that the sulphate of lime has been formed subsequently to the 

 deposition of the strata of limest9ne in which it is found, and that it may belong to that class 

 of bodies whose formation is continually going on. The decomposition of the sulphuret of 

 iron, and the subsequent action of the sulphuric acid thus produced upon limestone, has by 

 some been proposed as the mode in which this is accomplished. But a formidable objection 

 to Uiis view is, that iron pyrites, although a very common mineral, is not yet found in sufficient 

 quantity to account for the vast results which have been ascribed to it. Thus in the western 

 part of New-York, the occurrence of gypsum, the formation of vast beds of iron ore, and the 

 production of the immense number of sulphur springs which are known to exist there, have 

 all been referred to the decomposition of this single mineral. 



If all these phenomena were really due to the decomposition of iron pyrites, it would be 

 fair to infer that this substance existed in enormous quantities ; and that beds of oxide of iron, 

 resulting from this decomposition, should uniformly be found in the immediate vicinity of our 

 plaster beds and sulphur springs. But the facts in these cases do not accord with the theory. 



As all our sulphur springs contain sulphate of lime, and as they are most numerous and 

 copious in those parts of the State where gypsum beds abound, it may, I think, without vio- 

 lence, be supposed that the production of gypsum, and the evolution of sulphuretted hydrogen. 



