324 GEOLOGY. 



the principles which have heretofore been set forth, it is clear that 

 they must rest unconformably on formations older than the Cambrian, 

 where such formations constitute their substratum. 



As originally deposited, the Ordovician beds probably dipped 

 away from such lands as then existed. Thus on the south side of 

 the land of northern Wisconsin (Fig. 136), the Ordovician sediments 

 must have dipped slightly to the south, and on the east and west sides, 

 to the east and west respectively. The same relations must have 

 held originally about the Adirondacks, and about every other land 

 area from the borders of which the sea-bottom declined. Over great 

 areas in the interior, 1 this original and simple plan of stratigraphy 

 has been but little modified. 



In other regions, deformation of the strata subsequent to their 

 deposition has completely changed their position. Thus in the Appa- 

 lachian mountains, where the sediments were derived principally from 

 the land to the east, and where the beds doubtless had a slight dip 

 to the west at the time of their deposition, they now dip in various 

 directions and at various angles, some of them being nearly vertical. 

 Faulting has complicated their relations still further (Figs. 137, 138, 

 and 139) ? The same is true of the formations of the system along 

 the eastern border of New York and the western borders of the states 

 adjacent on the east. 3 The strata are in similar positions in some 

 parts of Arkansas 4 (Fig. 140), Indian Territory, 5 Oklahoma, and in 

 various mountain ranges of the Cordilleran system. 6 Even where the 

 beds are not folded, they are sometimes affected by faulting. 



Present condition of the formations. — Aside from the changes in 

 position which the Ordovician beds have suffered, as noted above, the 

 sediments as originally deposited have undergone more or less altera- 

 tion. In some cases the change has been slight, and in others great. 

 Many of the beds of sand and mud have been simply compacted and 

 cemented; indeed the greater part of the Ordovician sands are still 



1 See footnote, p. 319. 



2 For references, see p. 315. 



3 Walcott, The Taconic system of Emmons, etc., Am. Jour. Sci., Vol. XXXV, 

 1888. Also Merrill, New York City folio, U. S. Geol. Surv. 



4 Geological Reports of Arkansas, especially reports of 1890. Vols. I (Penrose) 

 and IV (Hopkins). 



5 See references on p. 319. 



6 See references on p. 318. 



