3i8. ROLLIN T. CHAM BERLIN 



tween the Cambrian and Ordovician in Bohemia, in certain parts 

 of the Armorican massif/ in the north of Wales,^ in Norway,^ and 

 at Spiti in the Himalayas/ but no clear evidence of important 

 folding appears. It is not clear that any one of these unconformities 

 is of the higher order; they seem rather to be intercurrent move- 

 ments of the minor order in what was, in general, a time of crustal 

 quiescence. In general much hesitation and indecision has been 

 shown by geologists in determining where to draw the dividing line 

 in the transition series between the Cambrian and the Ordovician. 

 In this study it is the periods of pronounced crustal crumpling, or 

 of marked differential movement, that are especially sought as 

 unequivocal representatives of events of the first order of impor- 

 tance; for unconformities of the simpler order are liable to represent 

 events of a minor order of importance. Judged by this rather 

 severe standard, the transition from the Cambrian to the Ordovician 

 was relatively quiet; it does not now appear that there were pro- 

 nounced crustal movements, and hence, on the basis chosen, it does 

 not seem clear that the two were sharply separated periods in the 

 earth's history. Throughout most of the globe where evidence is 

 available, there was no radical change in the areas or the atti- 

 tudes of sedimentation. This indecisiveness in the character of the 

 diastrophic movements associated with the close of the Cambrian 

 and the opening of the Ordovician leaves the question of the 

 separateness of the two as distinct periods a somewhat open one 

 considered from the diastrophic basis simply. 



ORDOVICIDES 



The greater part of the Ordovician period seems to have been 

 a time of crustal quiescence, in the sense of the term used in this 

 discussion, but its closing stages were marked by pronounced dis- 

 turbances in various portions of the globe. These are the first 

 crustal deformations of the higher order for which I have found 

 clear evidence since the close of the Proterozoic. 



^ Emile Haug, Traite de geologic , II (191 1), 634-35. 

 ^ A. J. Jukes-Browne, The Building of the British Isles (191 1), p. 78. 

 3 Eduard Suess, The Face of the Earth, Sollas trans., II (1906), 52. 

 ^ A. de Lapparent, Traite de geologic, 5th ed., II (1906), 808. 



