J. D. Dana on Cohesive Attraction* 381 



than vertically, will often cause such concretions to be flat ; and 

 when they become very numerous, a bed of concretions is 

 changed to a solid bed of compact rock. 



In still other cases, a molecular change of the same general 

 character and on the same principle, goes on after consolidation 

 has taken place. 



The structure of such concretions must depend on the ma- 

 terial constituting them. The mode of formation, and the gen- 

 eral property that attraction has a definite relation to distance from 



a centre, will give them a similarity of character, in correspond- 



ing parts. The constituent crystalline grains, when any are ap- 

 parent, will have necessarily a corresponding position with refer- 

 ence to the centre. A foliated mineral which in one part had the 

 toliation concentric in the spherical mass, would have for the rea- 

 son stated, the foliation concentric throughout ; and a fibrous min- 

 eral, with the fibres radiating from the centre, would retain this 

 structure regularly.* 

 These considerations sustain the conclusion, that 

 -X- V II. Cohesive attraction produces spherical concretions, about 

 a c *uster of molecules as a nucleus, through the tendency of mole- 

 cular action or condition to propagate itself; and concentric ag- 

 gregations begun, act under the general influence of the radial 

 action of attraction in a mass, which action, other things the 

 same, is equal at equal distances from a centre. 



We might consider other effects of cohesive attraction, and ex- 

 tend our remarks to liquids and gases. But this paper has already 

 bached an undesired length, although giving but the outlines of 

 a subject that admits of great extension ; and the consideration 

 ?f liquids and gases in the present state of our knowledge would 

 involve us in speculations that we have purposely endeavored to 

 avoid. 



We have thus endeavored to follow out the various facts pre- 

 sented by matter as it exists around us. Observation has proved 

 m ore profitable than closet speculation in animal and vegetable 

 Physiology ; and so it will be with regard to the grand organizing 

 force of the so-called inorganic kingdom,— the basis of Mineral 

 Physiology. The fact that the attraction of molecules is liable 

 to modifications of condition, and especially the simple yet fixed 

 relations between these modifications, nothing but a crystal could 

 toake known to us. Yet the principle is as wide as the universe 

 * its application ; for we live in a universe of molecules, and all 

 the grandeur of physical nature is the result of molecular forces. 



.* The concentric structure here explained is analogous in many respects to the 

 circular and spherical forms in vegetation. The growing lichen extends itself cir- 

 cularly, owing to progressive assimilation or development. This proves no simi- 

 larity of nature between the organic forces and cohesive attraction; it only shows 

 that different forces act under a common law. 



