T. STERRY HUNT. 49-< 19) 



position of the uncrystalline strata ; the formation of 

 which thus involves the decay of vast masses of the crys- 

 talline rocks. 



If we follow into the southern states of the Union the 

 great Atlantic belt of ancient crystalline rocks, we shall 

 find that these, which in New England and New York 

 are either bare and ice-worn, or else covered with trans- 

 ported materia], are there concealed beneath a cover 

 often one hundred feet or more in thickness, of decayed 

 material, which, although it has lost one-half or more of 

 its weight, still retains its original volume, structure and 

 place, and in its deeper portions includes lumps or cores 

 of crystalline rock still undecayed. It needs but the 

 action of water, such as would result from a gradual sub- 

 mergence beneath an invading sea, to break up these soft- 

 ened rocks, carrying off the clay to be laid down in quiet 

 waters, dejDositing the sand in the track of the currents, 

 and leaving behind the cores of undecayed rock in the 

 shape of boulders of granite or gneiss — thus producing 

 all the conditions to be seen in our more northern regions, 

 where a denuding process has disturbed and rearranged 

 the results of the sub-aerial decay of the ancient rocks. 



That such has been the origin of the mechanical sedi- 

 ments which make up the great bulk of the stratified 

 rocks from the Eozoic age to our own, there can be no 

 doubt, and the history of our granite boulders is clear in 

 the light of these observations. The hard, undecayed 

 crystalline rocks are not readily worn away, but the pre- 

 liminary process of decay makes the action of eroding 

 agents easy and rapid. Hence it is that in the northern 

 regions, where marine currents and glacial action have 

 done their work, the decayed materials have long since 

 been swept away from the surface of our hills, and that 

 only here and there, in localities sheltered from the ero- 

 ding agents, as, for example, along the western base of 

 Hoosic Mountain in Massachusetts, do we find any re- 

 mains of the deep mantle of decayed rocks which once 

 covered our northern hills of gneiss and granite. But 

 when we go southward from Philadelphia, beyond the 

 southern limit of glaciation, we hud the covering of de- 

 cayed rock lying deep over the Blue Ridge, in Virginia 

 and the Carolinas. It would be long to tell the evidence 

 that in past ages this condition of things extended over 



