CLAYSTONES. 241 



We defer a description of these nodules to that part of our Report which treats of the 

 unstratified rocks. So also we do of the nodular masses found in a few dikes of trap 

 rocks. But there are two sorts of concretion in alluvial clay, whose description appro- 

 priately follows the more recent deposits. 



There is a third substance that not unfrequently occurs in the form of small concretions 

 in low grounds. It is an oxyd of manganese, called Wad. This is derived from the 

 rocks by means of water, and deposited, like bog iron ore, in swamps. It occurs not un- 

 frequently in the State. 



I. CYLINDRICAL FERRUGINOUS CONCRETIONS. 





 These are the first variety which we shall notice. They occur generally in the upper 



part of the clay, where it begins to take sand into combination. They consist generally 

 of small cylinders, which sometimes have a spheroidal head, larger than the stem. They 

 are always peforated longitudinally, though the opening is often quite small. They stand 

 perpendicularly in the deposit, and the cementing material appears to be iron. They are 

 sometimes quite hard, but generally are easily broken. They have been regarded by 

 some as fossils ; but the more probable opinion is that they are concretions, formed around 

 the roots of certain plants (e. g. species of Equisetum.) Prof. Adams deposited in the 

 State Cabinet, which Avas burnt, nearly four hundred specimens from Colchester, and Ap- 

 pletree Bay in Burlington. But there is a duplicate set in the collection which he pro- 

 cured for himself, and presented to Amherst College. We have not deemed it important, 

 however, to give sketches of any of these, since these would not cast any light upon their 

 character or origin. We can only say that organic matter, such as the roots of plants, 

 seems to exert an influence in some circumstances for the production of concretions. 



II. CLAYSTONES. 



These are the most abundant and remarkable of the concretions found in Vermont. 

 Some very striking varieties occur there, which we have seen nowhere else. These bodies 

 are generally known by the name of claystones. They occur in clay, and have the color 

 of the clay in which they are found. They are in fact clay which is cemented by carbon- 

 ate of lime. Sometimes they are complete spheres, which is in fact the normal shape of 

 concretions, where the matter composing them is equally free to move in all directions and 

 obeys the force of attraction at the center. But generally these conditions were wanting, 

 and the claystones are flattened and made to assume almost every possible shape. A 

 prevalent opinion is, that they have been worn into their present forms by water, because 

 water washes them out of the clay banks where they were formed. But nothing is more 

 absurd than to impute their shapes to the mechanical action of water. They are produced 

 chemically, in clay made plastic by water, and probably holding in solution the carbonate 

 of lime, by which they are cemented. 



