42 REPORT OF THE 



sand feet. We have thus the materials for several geological 

 formations, each with its own mineral characters, and em- 

 bracing the organic debris which characterized its own age. 

 Through some appropriate agency these sediments become 

 solidified. But at length some movements begin to be expe- 

 rienced by the solid crust of the earth, and our horizontal strata 

 begin to be elevated in one place and depressed in another 

 Here is a dome shaped bulge, and there is a long ridge, rising 

 in some of its parts above the surface of the sea. Successive 

 disturbances increase the inequalities, and at length our level 

 sea-floor presents all the irregularities of a carpet carelessly 

 thrown down. By degrees the general uplift of the sea bottom 

 has made an extensive addition to the continent. 



Thus far we suppose each successive layer of rock to be con- 

 tinuous over every ridge and through every valley. But now 

 we must consider the effect of denuding forces — those farces 

 which move over the surface, and plane down the inequalities. 

 Whether these results are attributable to the action of the 

 atmosphere, frost, glaciers, powerful currents of an invading 

 sea, floating icebergs, or to all of these agencies combined, or 

 in succession, cannot here be considered. It is sufficient to 

 know that such forces have acted, and that all the original ele- 

 vations have been more or less worn down, and the rubbish 

 produced strewn over the general surface, tending still further 

 to obliterate its unevenness. Consider what would be the 

 effect of paring off the summits of the ridges and domes of up- 

 raised strata. The uppermost layer would be sliced through, 

 and the second in order would come in sight. Then the wear- 

 ing would continue till the second layer would be cut through, 

 and the third would appear. So, in some cases, the denudation 

 has continued, till thousands of feet of strata have been pared 

 off, and the underlying granite has been exposed; and then this 

 has been planed down some hundreds of feet Glance now at 

 the cut edges of the strata. The lowest rock reached will be 

 found in the center of the dome, or along the eentral axis of 

 the ridge. If it is a dome, the overlyiag strata dip in all direc- 



