26 



from the liquid, and thus the cause of the hardness of the water is in 

 a great degree removed. It is obvious from these facts, that the wa- 

 ter obtained from strata of gravel, sand or pure clay, will in general 

 be purest and most suitable for employment in the arts. As an ex- 

 ample of the kind of impregnation usual in the water of this district, 

 I subjoin the results of an analysis of the contents of a spring in 

 James City county, near Williamsburg. In 400 cubic inches of this 

 water, the aggregate of solid matter was found to be 104.49 grs. 

 consisting of the following substances, viz: 



Muriate of soda, 



49.84 



Muriate of lime, 



15.08 



Carbonate oflime, 



26.73 



Sulphate of lime, 



6.24 



Silica and alumina, 



4.00 



Sulphate of soda, 



0.25 



Ammonia, 



a trace. 



Organic matter, 



1.00 



Loss, 



1.75 



104.49 

 The large proportion of Muri. soda shown to be present in the 

 above instance, is an interesting fact, particularly when taken in 

 connexion with the locality whence the water was procured. For, 

 it cannot be considered probable that this ingredient could be de- 

 rived from the neighbouring rivers or the bay, as this would imply 

 an extent of filtration in a horizontal and upward direction, which 

 it would be unphilosophical to admit. It is rather, as I conceive, to 

 be looked upon as referable to the former impregnation of saline 

 matter derived from the waters of the ocean, beneath which nearly 

 all the strata of this region were originally deposited. 



NATURE AND VARIETIES OP THB MIOCENE SHELL MARL. 



In the general description of the district of which we are now 

 treating, a detailed account has been given of the arrangement of 

 the beds of fossils as they occur in nearly all the localities which 

 have been examined, accompanied by an enumeration of the princi- 

 pal shells, an account of the materials in which they are embedded, 

 and with which they are associated in contiguous strata. We are 

 next to consider the materials of these beds in relation to their agri- 

 cultural importance, and to exhibit the relative value of the marl of 



