Address before the Association of American Geologists. 261 
ent centres of attraction existed in the clay, it is not difficult to 
conceive how. all the varieties-of form assumed by the concre- 
tious, may have been produced by a modification of circumstan- 
ces. I find, that as in crystals of minerals, certain forms predom- 
inate at particular localities, so it is with the claystones. And 
finally, I am led by all the facts to the conclusion, that these con- 
cretions are produced by laws as fixed and definite as those of 
crystallography. To discover and develop these laws, therefore, 
must be an object of great interest. 
There is another interesting concretion in the same diluvial 
clay, in all parts of our country, consisting generally of concen- 
tric alternating layers of clay or loam, and the same material more 
or less colored and consolidated by the hydrate of iron. The axis 
consists usually of the root of a vegetable, or some other organic 
dy. Portions of the same clay are sometimes crossed by par- 
allel divisional ‘planes, so as to: produce. rhomboidal prisms, pre- 
cisely like those in the older consolidated rocks, which have usu- 
ally been referred: to the: agency of heat. Bae this clay - 
probably, never have be 
must resort to some other explanation of this jointed PO 
‘And since the experiment of Mr. Robert Weare Fox ‘OX upon the in- 
fluence of galvanism upon clay, I can hardly doubt but this agen- 
cy might have produced it, and also the ferruginous concretions 
that have been described, and perhaps have aided in forming the 
claystones. But to settle these points will require numerous ob- 
servations and experiments; and my chief object in these re- 
marks is to show that this is a ——- page long ac ceecigre 
field of research. 
wiitis, incase in } many of aes state surveys, that: particular at- 
tention will be given to the connection between geology and ag- 
ticulture. T'o-do this, the geologist is obliged to callin the aid 
of organic and analytical chemistry; obviously the most difficult 
branches of that most useful science. Hence the analysis of 
Soils, of the plants which they produce, and of the various fertili- 
zers which are applied by the farmer, as well as of the rocks 
whose disintegration produces the soil, ought to form the objects 
of a commission distinct from that of ordinary geology : and I 
hope the time is not far distant, when such an office will exist in 
all the states of the Union. For although we ought not to look 
foristriking benefits fromsuch-a work so soon as from a geologi- 
