22 DECOMPOSITION OF GNEISS. [CHAP. XXI. 



region. Yet it is striking around Milledgeville, 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, measured twelve feet in its 

 longest diameter, and was four feet high. I pre 

 sume 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 w r hen 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 lati 

 tude 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. 



Another most singular phenomenon in the environs 

 of Milledgeville is the depth to which the gneiss and 

 mica schist have decomposed in situ. Some very in 

 structive sections of the disintegrated rocks have been 



O 



laid open in the precipices of recently formed ravines. 

 Were it not that the original intersectinGf veins of 



c&amp;gt; o 



white quartz remain unaltered to show that the 

 layers of sand, clay, and loam are mere laminae of 

 gneiss and mica schist, resolved into their elements, a 

 geologist would suppose that they were ordinary 

 alternations of sandy and clayey beds with occasional 

 cross stratification, the whole just in the state in 

 which they were first deposited. Now and then, as 

 if to confirm the deception, a large crystal of felspar, 



