Address before the Association of American Geologists. 261 



eiit centres of attraction existed in the clay, it is not difiicnlt to 

 conceive how all the varieties of form assnmed by the concre- 

 tions, may have been prodnced 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 

 body. 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. But this clay can, 

 probably, never have been even sun-dried ; and, therefore, we 

 must resort to some other explanation of this jointed structure. 

 And since the experiment of Mr. Robert Weare Fox 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 promising, though long neglected 

 field of research. 



It is expected in many of the state surveys, that particular at- 

 tention will be given to the connection between geology and ag- 

 riculture. To do this, the geologist is obliged to call in the aid 

 of organic and analytical chemistry ; obviously the most diflicult 

 branches of that most useful science. Hence the analysis of 

 soils, of the y)lants 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 

 for striking benefits from such a work so soon as from a geologi- 



