Recent compilations of data concerning orogenic and epirogenic movements of the earth's crust, especially by Stille and Bucher, strongly support the conclusion that both of these types of crustal deformation are markedly periodic and that they are related. Times of essential stability of the crust during which sedimentation proceeds uninterruptedly in many regions alternate with times of crustal unrest in which orogenic movements may contemporaneously affect certain widely separated geosynclinal belts but fail to affect others. The chief marine transgressions of continents occur during epochs of general crustal stability. The making of widespread disconformities in areas not affected by orogenic movements appears to coincide in time with the occurrence of orogenic disturb nces in geosynclines.

Stille recognizes six epochs of more or less well defined orogenic disturbance and accompanying crustal unrest in the post-Devonian part of the Paleozoic era. These are (1) Bretonian, post-Devonian pre-Dinantian, (2) Sudetian, post-Dinantian pre-Namurian, (3) Erzgebirgian, mid-Namurian, (4) Asturian, post-Westphalian pre-Stephanian, (5) Saalian, post-Early Rotliegende pre-Late Rotliegende, and (6) Pfalzian, post-Permian pre-Triassic. Excepting numbers 1 and 6, however, the indicated disturbances do not coincide with period boundaries as now commonly defined.

The present paper reviews evidences primarily from North American areas bearing on the age of Late Paleozoic crustal movements and compares this record with that of Europe. At least nine series that are separable on the basis of structural and paleontologic criteria appear to be recognizable in the post-Devonian section of North America. The breaks between these stratigraphic series or "blocks" represent orogenic or epirogenic movements. In general, it appears that times of orogenic movement in Europe are matched by epirogenic movements in North America and conversely that orogeny in America may be represented by epirogeny in Europe.