402 ' C. Schuchert — Paleozoic Crustal Instability 



more and more into recognition, and it is inevitable that 

 some system of naming them will be adopted by geolo- 

 gists. Sometimes a single region is affected, as is the 

 case in the minor late Ordovician orogeny known as the 

 Taconic, when eastern North America was folded from 

 about Pennsylvania northeastward across Newfoundland, 

 a distance of upward of 1300 miles. At other times, more 

 than one continent was folded, as was the case in the 

 major orogeny that took place toward the close of the 

 Paleozoic, or the more recent ones of Mesozoic and Ceno- 

 zoic times. We therefore see that the shrinkages taken 

 up by the orogenies differ in their power to fold the litho- 

 sphere, and in their geographic extent. Whether they 

 can be grouped into two or more categories so as to be of 

 value in delimiting periods and eras of time, or whether 

 they have all gradations of strength between the lesser 

 (the disturbances) and the greater ones (the revolutions), 

 is a most interesting problem of which more will be said 

 in the conclusion of this paper. 



The writer holds that the crustal deformation of a given 

 time and region should have an independent name, and 

 that this term should be applied to all of the chains of 

 mountains comprised in the region of identical movement. 

 On the other hand, there has been synchronous or nearly 

 synchronous orogenic work going on in different conti- 

 nents, or in different parts of the same continent, or in 

 succession on either side of an oceanic basin or orogenic 

 realm. To all of these independent provincial orogenies 

 it is proposed eventually to give distinct geographic 

 names. 



In addition to the epeirogenic and orogenic movements 

 of the continents, there are the gradual warping deforma- 

 tions known as the bradyseisms (from the Greek words 

 bradus and seismos, meaning slow earthquake), but as to 

 the significance and terminology of these gentle move- 

 ments nothing will be said at the present time. 



Finally, it seems to be advisable that in Historical Geol- 

 ogy all of the orogenies of a period of time be grouped 

 under a distinctive term. The speaker did this in his 

 text-book, using geographic names of broad areas, as Cas- 

 cadian, Grand Canyon, etc. A better terminology was, 

 however, invented earlier by T. C. Chamberlin and ably 

 seconded by his son Rollin in the terms Devonides, Silur- 

 ides, etc., and it is this latter method that we had best 

 agree upon. 



