122 Canadian Record of Science. 



belts along the seashore, and along the lake shores 

 (Ontario and Erie) ; — we should expect the supposed dune 

 belt to carry fossils in its Upper portion since it was mani- 

 festly transgressed by the ocean. 



During the course of time the rate of depression may 

 vary to the opposite sense, i. e., the land may begin to rise. 

 Under these circumstances the landward end of the strata 

 previously deposited will be subjected to erosion. During 

 a subsequent depression the new deposits would rest un- 

 comformably upon them, while further seaward, where 

 the earlier deposits had not emerged, there would be 

 structural conformability. Such conditions seem to have 

 existed during a portion of Palaeozoic time in eastern and 

 central North America, where, in the east, unconformities 

 are found between the various formations making up the 

 Palaeozoic series, while further west the various members 

 of the whole series are found with the younger conform- 

 ably overlying the older, indicative of the fact that there 

 was here continuous deposition. 



Eelatively slight variations of either factor, alone, or 

 of both in opposite senses willl produce interdigitation of 

 the three principal members along the lines of the transi- 

 tion zones. 



The individual consideration of the remaining combi- 

 nations is unnecessary as the final results will be similar 

 to those produced by the variations already considered. 

 Inequalities in the supply of material in the different 

 zones to synchronous portions of the same bed (or series 

 of beds), will lead to many irregularities in the thickness 

 of the bed in its different parts. The final product may 

 thus be very complex, though the general principles will 

 still be applicable. 



In the previous discussion it has been tacitly assumed 

 that the material supplied from the oldland area is of such 

 a nature that all three zones, including their transition 

 phases, will receive each its quota of deposit. Material 

 suitable to fulfil this condition will normally be supplied 



