PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 809 



forgotten. To American science is due the discovery of the true 

 laws of mountain structure. The Messrs. Rogers and their assist- 

 ants in Pennsylvania first showed, by careful topographical studies, 

 the laws which govern the structure of the Appalachians ; and 

 Prof James Hall subsequently explained the origin of these moun- 

 tains by showing their relation to sedimentary accumulation, and 

 to oceanic currents. These views are now being adopted by Euro- 

 pean geologists, who have learned from our investigations of the 

 Appalachians to understand their own mountain systems. 



Law of Ge:ological Progress. 

 The great forces which build up the world are slow and uniform 

 in their action. Continents have sunken and risen, as they now 

 sink and rise, so slowly that a single lifetime is too short to detect 

 the changes. Nature's economy has been uniform, and the con- 

 vulsions, deluges and cataclysms by which some would explain 

 geological phenomena, have had no existence, or are but local 

 accidents of no general significance. 



Imperfection of the Geological Record. 

 Each new discovery shows us the imperfection of the geological 

 record, by supplying some page Avhose absence had before been 

 unsuspected. Thus, in the New York series, we have learned that 

 between the adjacent and comfortable calciferous sandrock and the 

 Chaz}'^ limestone, there intervened a lapse of time represented in 

 the adjacent ocean by many thousand feet of fossiliferous strata, 

 which afford a transition between these two contiguous but widely 

 dissimilar formations. In like manner we have evidence that 

 between the Laurentian gneiss of the Adirondacks and the Potts- 

 dam sandstone which covers their base, immense formations inter- 

 vened, some local in their disposition, and others more widely 

 spread, of which only vestiges here and there remain. While the 

 history of nations is written, for the most part in imperishable 

 records, that of by-gone geologic periods was recorded in the rock 

 formations, which have, by slow destroying agencies, been broken 

 np and served to form new formations, written over with new 

 characters. 



Flexible Copper Tube. 



Mr. S. H. Maynard exhi))ited a specimen of flexible copper tube 

 made at the Columbian metal works. A cast ingot is so pressed by 

 rollers that it loses its crystalline form, assuming a laminated ap- 

 pearance, and thus becomes very flexible. 



