144 NEW YORK STATE MUSEUM 



lies symmetric to the whole arrangement and with the Cincin- 

 nati uplift it is on the line of symmetry. It is possible that this 

 Michigan basin, instead of being an independent depression, 

 originated from the same warping force as the Cincinnati up- 

 lift, being the result of a longitudinal oscillation of the axis of 

 the same geanticline, comparable to those more intensive longi- 

 tudinal oscillations of the axes, which have been observed in 

 some of the Alpine folds \_see Haug, Traite p. 211]. The Cana- 

 dian geologists, however, have claimed to find the influence of 

 the Cincinnati uplift extending from the west end of Lake Erie 

 further north to Lake Huron. In this case it would seem that 

 the Atlantic pressure had affected the entire extent of the up- 

 lift [see p. 145] giving it a direction subparallel to the 

 Appalachian folds, and the Michigan basin would have to be 

 considered as independent of the Cincinnati uplift, a view distinctly 

 not supported by the general distribution of the formations around 

 the basin. 



The development of these symmetric structures may have taken 

 place as shown in charts II and III. In chart II the Canadian 

 shield A and its Paleozoic platform are outlined, the two sep- 

 arated by the line M-N. First then, an extensive depression 

 affected the middle portion of the platform producing the Paleo- 

 zoic eastern basin B, and leaving two long embracing arms 

 standing, the western one D and the eastern one E. A slight 

 depression had also taken place in the northern slope [C] which 

 finds its expression in the Hudson Bay embayment. Since 

 this and the eastern basin lie with their longitudinal axes on the 

 same line (meridian), the idea that they may be expressions of 

 the same warping movement, is worthy of some consideration. 

 In its favor could be mentioned the fact that a path of migration 

 is postulated along this line for the Niagaran fauna by Weller 

 and a Devonic embayment by Schuchert. It will be noticed 

 [see chart II] that the Hudson Bay Devonic embayment [C] and 

 the Michigan basin approach so much that only a relatively 

 narrow Precambric belt separates them, upon which, moreover, 

 still a small Paleozoic outlier (n.e. of Georgian bay) remains. 

 It is therefore quite probable that temporary depressions ex- 

 tended there across the protaxis, and that the resulting Siluric 

 and Devonic rocks have disappeared again by erosion. 



Chart III illustrates the changes which next took place in 

 the two arms and in the inclosed basin. The arms were broken 



