180 



Scientific Geology. 



ore, are only impure varieties of hydrate of iron. And the bog 

 ore is daily forming before oar eyes by aqueous deposition, and 

 some of it is in fact the same as the compact brown oxide. Only ad- 

 mit, then, that circumstances were favorable to crystallization, when 

 the hematite was in a state of solution in the water percolating 

 through clay, and may we not conceive how that ore was produced ? 



The oxide of manganese, sometimes delicately radiated, and some- 

 times investing the hematite, occurs at probably all the beds of hy- 

 drate of iron that have been mentioned. I noticed it particularly at 

 the bed in W est Stockbridge : and it is well known that it did exist in 

 Bennington, Vt. in the same connection, in large quantity. 



Associated with the hydrate of iron in Richmond, in a bed owned 

 by Mr. Gates, there has been found a hydrate of alumina, (alumina, 

 64. 8, water, 34. 7,) which Professor Torrey has named Gibbsite, in 

 honor of Col. George Gibbs, one of the earliest cultivators, and most 

 munificent patrons of mineralogy in our country. It occurs mamil- 

 lary and stalactical, of a white color. It may be obtained there abun- 

 dantly ; and a single specimen has been found in Lenox. 



The nodular argillaceous oxide of iron and yellow ochre occur 

 occasionally in the tertiary region around Boston, particularly in 

 Charlestown and Cambridge. 



Concretionary Carboitate of Lime. 



In the clay beds of the Connecticut valley, a curious concretion 

 occurs, which has received the name of claystone, from its resem- 

 blance to indurated clay, that has been rounded by the action of wa- 

 ter. Indeed, I did not till recently suspect the presence of carbonate 

 of lime: but the application of an acid produces considerable effer- 

 vescence. The general shape of these concretions is that of an oblate 

 spheroid, sometimes so flattened as to become lenticular, and some- 

 times nearly spherical. These spheroids are usually joined together 

 with considerable strength. They vary in size from two inches, 

 down to that of the smallest pigeon shot, and some of these smallest 

 are so numerously strung together, as to become decidedly botryoidal. 

 In other instances, the spheroids are so intimately blended, that there 

 are no interstices between them ; and only slight convexities are ex- 

 hibited, in relief, on the surface. Not unfrequently that surface is 

 studded with minute spheroids, not larger than the head of a pin. 

 Sometimes the concretion is not spheroidal, but simply an irregular 

 plate, often several inches across. In no case does the thickness of 



