1847.] Association of Geologists and JVaturalists. 201 



There is, in the mastodon, a remarkable preponderance of the an- 

 terior over the posterior extremities. The upper part of the head 

 is more flattened, and the facial angle less than in the elephant, 

 and the cavity of the cranium is less. The bones of the cranium 

 are fdled with large cells, probably to ensure lightness; the nasal 

 cavity and the proboscis resemble those of the elephant. He en- 

 tered into a careful comparison of the teeth in these tv^'o ani- 

 mals, showing many interesting analogies. He alluded to the 

 remarkably sound condition of the bones, which he attributed 

 chiefly to their being excluded from the air, and having been 

 preserved in- marl. Some are silicified, others ferruginated. 



It is impossible to determine the cause or time of the disap- 

 pearance of this animal; but it was not, certainly, at some gene- 

 ral catastrophe. History and tradition are silent on this subject. 

 The period of their disappearance was at least, as far as history 

 goes, one thousand years ago. 



Prof. Agassiz remarked, how gratifying it must be to natural- 

 ists, to be able to examine the bones themselves, instead of fan- 

 ciful representations of them; and to be able to compare them 

 with those of the elephant, both old and young. 



On the Laws of Cohesive Mtraction, by Prof Dana. 



He remarked that solidification and crystallization are the 

 same. He instanced ice, snow, steel, granite, &c. If so, then 

 the laws of solidification are the laws of cohesive attraction. 

 Each species of matter has a distinct characteristic crystallization; 

 molecules have the same axis as the resulting form. 



His inferences from the facts brought forward, were: 



1. Cohesive attraction is characterized by fixed angles, as re- 

 gards the direction of its action, and by specific relations of force 

 in certain axial directions — different in different substances. 



2. In the aggregation of molecules by attraction, only equal 

 homologous axes unite. 



3. The axes of cohesive attraction in molecules have opposite 

 polarity at opposite extremities. 



4. The polarity of molecules may be reversed by extrinsic in- 

 fluence. 



5. The axis and polarity of cohesive attraction exist before the 

 union of the molecules, instead of being a consequence of that 

 union. 



6. The axial lines of cohesive attraction are not indefinitely 

 fixed in position, but are modified in direction and force by tem- 

 perature. 



7. The variations which the attraction of cohesion undergoes 

 take place according to some simple ratio. 



