Á phen omenon of the most extraordinary eharacter haa recently been in progresa in the vioiuity of the natural bridge in Virginia. From recent information from that soction it seems that struoturo is in imminent danger of destruction. - Some tiinn since a gentleman who had oooasion to cross the bridge observed, upon glancing into the chaain below, a vapor issuing from some orovices on the western side of the bridge, and detected a peculiar odor in tho atmosphere. Having occasion to visit tho vicinity on the following day, tho gentleman found matters in the most exoited condition. Donsa clouds of black srnoko hnng in grotesquo forms over the scène, and the iuhabitants were in the wildest excitement. From below the bridge volumes of smoke were rolling continually, except when intcrrupted by jets of black flamo, and stoam, accompaniod by the peculiar odor of the previoua day, was isuing from tho fissures in the ground which had booome parched and oracked from the efieots of the heat. The rock on tho western side of the bridge had also beoome cracked by the heat, and oocasionally the crushing sound of aboulder could bo distinguished as it bacame detached and dashed into the water below, though tho aroh, as well as could be discerned in the intervals when the heavy volume of smoke would be swept aside by the wind, remained intact. In con?equence of this frightful condition of things the utmost excitement and confusión prevailed, and tho negroes and the superetitiously inclined were floeing from the vicinity in terror, evidently believing that an embryo volcano had burst from the ground boneath thein. The matter was referred for soluúon to Professor Campbell, of tho Geological department of the Washington College, Virginia, who was known to have made a geological examination of tho bridge some years since, and who ascribed the cause of the extraordinary combustión to one of the most natural cauaes. In a critieal oxamination of the foruiation of tho formatiou of tho bridge by that gentleman it was disoovored that it was composed of mountain limestone, with largo, h'asures filled with grahamite, which, as is well known, is a kind of bit uminous coal or asphaltura, doposited in seauis in foimiitiou3of this peculiar kind. At some distance above the high water mark sulphurous deposits and traces of metalic oxides were detected. The action of the sulpliur on the metalic oxides, even in small quantities in the presence of water, will genérate heat to a degi'ce abundantly suffioient to ignite a mass of as combustible a nature as grahamite. - So the phenomenon is attributed to the chemical action of the water, this agent having been supplied by the unusual depth of snow, which being molted caused the creek to be swollen to an unprecedented extent upon the geological formation of the bridge .