38 /. D. Whitney on the Ores of Iron in the Azoic System. "* 



by a force which permanently increases its length without at the 

 same time compressing it. 



Another effect of the lateral motion of the atoms of a soft 

 heavy body, when acted upon by a percussive force with a ham- 

 mer of small dimensions in comparison with the mass of metal, 

 — for example, if a large shaft of iron be hammered with an or- 

 dinary sledge, — is a tendency to expand the surface so as to 

 make it separate from the middle portions. The interior of the 

 mass by its own inertia becomes as it were an anvil, between 

 which and the hammer the exterior portions are stretched longi- 

 tudinally and transversely. I here exhibit to the Association a 

 piece of iron originally from a square bar four feet long, which 

 has been so hammered as to produce a perforation of the whole 

 length entirely through the axis. The bar could be seen through, 

 as if it were the tube of a telescope. 



This fact appears to me to be of great importance in a practi- 

 cal point of view, and may be connected with many of the la- 

 mentable accidents which have occurred in the brealdng of the 

 axles of locomotive engines. These, in all cases, ought to be 

 formed by rolling, and not with the hammer. 



The whole subject of the molecular constitution of matter 

 offers a rich field for investigation, and isolated facts, which are 

 familiar to almost every one when attentively studied, will be 

 made to yield results alike interesting to abstract science and 

 practical art. 



Art. VI. — On the Occurrence of the Ores of Iron in the Azoic 

 System ; by J. D. Whitney.* 



The object of the present communication is to call attention to 

 the geological position and mode of occurrence of one of the 

 most interesting and important classes of the ores of iron, namely, 

 those which are associated with rocks of the Azoic System. 



The term Azoic, first employed by Murchison and De Verneuil 

 in their description of the geology of the Scandinavian Peninsula, 

 has been adopted by Mr. Foster and myself in our Keports on 

 the Geology of the Lake Superior Land District, and has been 

 shown by us to be applied with propriety to a series of rocks 

 which covers an immense space in the Northwest. We have 

 called attention to the fact, that this system of rocks, wherever it 

 has been demonstrated to exist, has been found characterized by 

 the presence of deposits of ores of iron, developed on a scale of 

 magnitude beyond anything which occurs in any of the succeed- 

 ing geological groups or systems of rocks. 



* Proceedings of the American Association for the Advancement of Science, 

 Ninth Meeting, held at Providence, R. I., August, 1855, p. 209. 



