410 C: Schuchert — Paleozoic Grustal Instability 



plainian and late Lower Devonian times. From the evi- 

 dence cited and illustrated in the graphs (Figs. 1-5), we 

 therefore learn that there is some irregularity in the time 

 appearance of the disturbances. The few exceptions, 

 however, are not sufficiently striking to prove that the dis- 

 turbances have no value for the delimiting of the periods. 

 On the contrary, the great majority of the orogenies ap- 

 pear toward the close of the periods, and are variable in 

 the extent of the geographic areas affected. With a bet- 

 ter knowledge of the seemingly few erratic crustal pulsa- 

 tions, they may be seen to be either of decidedly minor 

 strength, or in some other way not to bear heavily against 

 the theory of regularity in the periodically recurring dias- 

 trophisms. "We therefore conclude that the great major- 

 ity of disturbances take place during the closing epoch of 

 the periods, that they are variable in their geographic 

 extent, and that the revolutions are made up of a series of 

 successive orogenies that finally bring on the critical 

 periods, resulting in the quickened evolution of the earth's 

 plants and animals. All of these conclusions are brought 

 out more clearly in their chronogenetic, spatial, and 

 marine-submergence relationships in the graphs, Figures 

 1 to 5, which should now be studied. 



EXPLANATIONS OF FIGUEES 



Fig. 1. — Diastrophism in Acadia in relation to time, space, and North 

 American marine submergences. Solid black pyramids indicate the time of 

 the orogenies and their geographic length in thousands of miles. Lined 

 pyramids, the time and spatial relations of the thick and coarse sediments 

 (oroclasmata). The amount of sea transgressions is in millions of square 

 miles. Spiral vertical lines indicate time and extent of marked discon- 

 formities. 



Fig. 2. — Diastrophism in Appalachia in relation to time, space, and North 

 American marine submergences. Eest of explanation as in fig. 1. 



Fig. 3. — Diastrophism in Llano in relation to time, space, and North 

 American marine submergences. Eest of explanation as in fig. 1. 



Figs. 4 and 5. — Diastrophism in eastern North America and western 

 Europe in relation to time, space, and North American marine submer- 

 gences. Eest of explanation as in fig. 1. 



