

GREEN-SAND. 469 



\ 



presented. It enables me to furnish more of what is valuable, be- 

 cause more certain than everything else I could offer, or than has 

 before been offered to the public on this subject prominent as it 

 has been made in the reports of the geological survey of Virginia. 



" New Haven, October 26, 1842. 



"Dear Sir The specimens of green-sand and accompanying earths have, 

 agreeably to your request, received my particular attention ; and I now 

 proceed to apprise you of the results at which I have arrived. 



" Commencing with the mechanical analysis of the green-sand, I was not 

 a little surprised to find that the green particles, when cleared by washing 

 of a slight investment of clay, assumed the aspect of chlorite and green 

 earth, and more rarely of grains of serpentine and fine scales of mica. The 

 other ingredients of the earth were chiefly grains of quartz (some of which 

 were penetrated by chlorite), and more rarely specks of garnet, iron pyrites, 

 and what appeared to be yellow phosphate of lime. Fragments of shells, 

 in a very decayed state, occur disseminated through the earth ; and I de- 

 tected also small teeth and bones of fishes. The proportions of the leading 

 ingredients are very difficult to establish with precision ; and after all my 

 examinations I can only give them approximatively, and within wide limits. 

 Thus, the quartz grains may be said to constitute from 60 to 80 per cent., 

 the chloritic and micaceous grains from 10 to 15 percent., and the fine clay 

 from 3 to 5 per cent. 



" Nothing is plainer than that the green particles possess the character 

 here attributed to them ; since they put on all the properties so common to 

 chlorite, being sometimes in regular hexagonal plates, though usually in 

 little granules made up of impalpable grains, which under the pestle easily 

 separate, with an oily feel, into bright green specks. Subjected to acids 

 and heat, it agrees with true chlorite. 



" The existence of such a mineral in the present formation offers nothing 

 remarkable in a geological point of view, since it may have originated in 

 the decomposition of chlorite slate rocks, or of veins in primitive rocks (in 

 which chlorite often abounds), and in both cases iron pyrites is its common 

 attendant. Besides, it may have been derived from the metamorphosis of 

 pyroxene, or from amygdaloidal traps, a source of green earth very often 

 recognised in Europe and America. Indeed, chlorite (which is but another 

 name for green talc) is often interchanged for mica, as an ingredient of 

 primitive rocks, and is everywhere little prone to decomposition, being, on . 

 the whole, one of the most persistent of the simple minerals. 



"Neither can it be objected that its chemical constitution is incompatible 

 with the results obtained for green earth ; for here we must bear in mind, 

 also, that it is impossible accurately to separate the green particles from 

 the mica, serpentine, and other ingredients with which they are associated. 



"M. Berthier found the following composition in the green grains from 

 the green-sand of Havre (France) 



Silica 50.00 



Protoxide of iron 21.00 



Alumina . 7.00 



Potassa 10.00 



Alumina 11.00 



99.00* 



" Mr. Seybert found in that of New Jersey 



* Geological Manual, by H. T. de fa Beche, Phila., 1832, p. 255. 

 40 



