CHAP. XXI. J BLOCKS OF GRANITE AND GNEISS. 27 



sea, and, like Macon, it stands on the boundary of the tertiary 

 and granitic region. Dr. J. R. Cotting, who had been employ 

 ed by the state to make a geological survey of part of Georgia, 

 showed me in the State House some fossils collected by him, and 

 he accompanied me in an excursion into the neighborhood of the 

 capital. It is well worthy of remark, that here, as every where 

 in Georgia and Alabama, there are loose blocks of granite and 

 gneiss strewed over the granitic area ; but no fragments of them 

 are ever seen to cross the boundary into the area composed of the 

 tertiary strata, where small pebbles only are seen washed out of 

 the sands. Farther to the north, in Massachusetts, for example, 

 and the island of Martha s Vineyard, we see enormous erratics of 

 granite, twenty-five and thirty feet in diameter, which must have 

 come from the north, probably from the mountains of New Hamp 

 shire, resting on the tertiary clays and rocks ;* and in Long 

 Island (New York), a variety of transported blocks repose upon, 

 or are interstratified with very modern deposits. In the south 

 ern states the same causes have not been in action, and if we 

 suppose icebergs to have been the transporting power in the north, 

 it seems natural that their action should not have extended to 

 the southern states, so as to carry fragments of crystalline rocks 

 out of the granitic region. Yet it is striking around Milledge- 

 ville, to see so many large detached and rounded boulders of 

 granite lying on the surface of the soil, and all strictly confined 

 within the limits of the granitic region. One of these, on the 

 slope of a hill three miles from the town, resting on gneiss, meas 

 ured twelve feet in its longest diameter, and was four feet high. 

 I presume that these boulders are nearly in situ ; they may have 

 constituted &quot; tors&quot; of granite, like those in Cornwall, fragments 

 of masses, once more extensive, left by denudation at a period 

 when the country was rising out of the sea, and fragments may 

 have been occasionally thrown down by the waves, and swept 

 to a small distance from their original sites. The latitude of 

 Milledgeville is 32 20 north, or considerably to the south of 

 the most southern limits to which the northern drift with its 

 erratics has hitherto been traced in the United States. 

 * Travels in N. America, vol. i. p. 259, chap. xii. 



