DIASTROPHISM AND THE FORMATIVE PROCESSES 519 



Where notable folding or faulting has taken place — and this is 

 common near the coasts — it may be possible to determine more 

 directly how far landward thicknesses of sediment of the order of 

 the ocean depth have once extended, for the upturned beds may 

 reveal them. Such observations must, however, usually give only 

 a minimum extension; the evidences of the maximum extension 

 have usually been cut away by erosion. An additional minimizing 

 effect usually arises from the compression and distortion of the 

 sediments under diastrophic thrusts. Their observed horizontal 

 breadth may be much short of their original depositional breadth. 



Students of terrestrial dynamics of all schools will probably 

 agree that the borders of the continents have been the seats of 

 exceptional folding and faulting. Observation and most theories, 

 however diverse otherwise, lend support to this view. It is prob- 

 ably safe, and even ultra-conservative, to take the innermost line 

 of continuous, thick, folded sediments as the landward border of the 

 outward-built terrace, if, of course, these sediments are later than 

 the time fixed upon as the beginning of the terrace-building epoch. 



As already remarked, it is useless at present to consider circum- 

 contineiital terraces older than the Paleozoic, for the metamor- 

 phisms and distortions of the earlier terranes and their wide 

 concealment forbid their treatment in any satisfactory way. None 

 the less, there is no good ground to doubt that the oceanward 

 borders of the Proterozoic lands were affected for long periods by 

 the process of terrace-building. The elastics form a notable factor 

 in the Proterozoic terranes; they form a factor, though a less 

 notable one, of the Archean also, and, under the planetesimal view, 

 of terranes below the visible Archean. Whatever, therefore, may 

 have been the original oceanward slopes of the submerged borders 

 of the continental nuclei during the very earliest eras, normal 

 topset and foreset slopes encircling these should have been acquired 

 during the progress of the Proterozoic era. Except, therefore, as 

 modified by diastrophism late in Proterozoic time or at its close, 

 the oceanward face of the continental masses should have borne 

 the normal sedimentary configurations. 



Regarding the effects of diastrophism, I think it will be agreed 

 quite generally that the mean results of long stretches of time tend 



