328 ANNUAL OF SCIENTIFIC DISCOVERY. 



with the underlying drift materials, or with abraded fragments of the rock 

 in place, as to give rise to a different character of soil in the valleys from 

 that of the elevated land. This valley soil, being much less homogeneous 

 in its composition, and containing a larger proportion of coarse materials 

 than that of the uplands, seems to have been adapted to the growth of for- 

 est vegetation; and in consequence of this, we find such localities covered 

 with an abundant growth of timber. 



" Wherever there has been a variation from the usual conditions of the 

 soil, on the prairie or in the river bottom, there is a corresponding change in 

 the character of the vegetation. Thus, on the prairies we sometimes meet 

 with ridges of coarse material, apparently deposits of drift, on which, from 

 some local cause, there has never been an accumulation of fine sediment; in 

 such localities we invariably find a growth of timber. This is the origin of 

 the groves scattered over the prairies, for whose isolated position and pecu- 

 liar circumstances of growth we are unable to account in any other way." 



ICEBERGS IN THE SOUTHERN OCEAN. 



Capt. Kirby, of the ship Uncoicah, from Xew York to San Francisco, re- 

 ports an encounter with a mass of ice off Cape Horn, Aug. 9th, immense, 

 almost beyond precedent, for the latitude. He states " that at first he could 

 not believe that it was ice, and, thinking he might have been drifted to the 

 northward during the several days in which he had not been able to get an 

 observation, set it down as an island covered with snow. The wind was 

 from the eastward, and the ship going at the rate of eight knots; she soon 

 brought the whole body above the horizon, and not long after the ice was 

 found to stretch along the whole head and on the weather bow. The course 

 of the ship was then altered, so as to bring the ice on the lee bow, and grad- 

 ually, as the bearings altered, five icebergs, of various sizes, were made out. 

 The ship passed within a few miles to the windward of them. 



" The ice-field and icebergs were estimated to be from eight to ten miles 

 long, and very high a solid mass of ice against which the sea broke, as 

 upon the iron-bound shores of a continent. At four miles distance, the 

 water about the ship was agitated with eddies and ripples, caused by the 

 opposing presence of so large a body to the usual ocean currents. The sides 

 along which the ship passed appeared to be precipitous up for more than a 

 hundred feet from the water, when they broke up towards the peaks in the 

 interior of the island; and down the steppes, the sp} r -glass showed the exist- 

 ence of great gullies and water-courses. When the sun shone full upon the 

 island, it reflected the light with great brilliancy." 



ON THE ORES OF ZINC AND MANGANESE FROM ARKANSAS. 



Dr. Win. Elderhorst has analyzed various specimens of Smithsonite from 

 the counties of Lawrence, Marion, and Independence. The principal mines 

 arc situated in Lawrence county; the principal ore is a massive, brownish- 

 yellow, cellular Smithsonite, occasionally sub-crystalline. The analyses of 

 average specimens show a very high per centage of oxide of zinc, varying 

 from 49 to 01 '7 per cent.; a very impure specimen, a mixture of carbonate 

 of zinc with clay, yielded 33 per cent, of oxide of zinc. The Arkansas ores, 

 therefore, compare very favorably with the best European ores, for example, 

 with those of Upper Silescia, the Rhenish workings, Belgium, Polonia, etc. 

 The ore occurs in dolomite, sometimes in regular veins, and firmly adhering 



