Theory of Formation of Sedimentary Deposits. 127 



this being especially true along the ancient shore-line 

 which probably emerged first. If the erosion continues 

 long enough, the complete series of products formed under 

 a certain series of uniform conditions may entirely dis- 

 appear, or, if the uplift is not great enough, only their 

 shoreward ends may vanish. 



In either case, their removal must expose the shore- 

 ward ends of strata belonging to an earlier cycle of 

 deposition. The later (as regards exposure, earlier as 

 regards deposition) deposits may themselves be also more 

 or less dissected, and the different portions remaining will 

 be thus more or less isolated. Such, indeed, seems to be 

 the relations existing between the limestones belonging to 

 the Trenton area, found in the Province of Ontario on 

 both sides of the Frontenac axis (and in New York State 

 to the south), and some of the associated sandstones which 

 were until quite recently usually designated Potsdam. 



Where these fragments of the old beds are distributed 

 along the line of the ancient land from which the material 

 was derived, it will happen that portions of synchronous 

 deposits occur in widely separated districts. For example, 

 a small amount of sandstone might remain in a protected 

 hollow near B (Figure 1.), and all the rest of the deposit 

 be eroded away, as far back as D, where the limestones 

 would form an infacing escarpment, the lower deposits 

 being covered with soil. The limestone, which was 

 synchronous with the sandstone left at B, may carry 

 fossils, while the small remnant of sandstone is destitute 

 of them, or carries forms of a different type, due to the 

 different environment when the forms were living, as 

 suggested in a preceding paragraph. 



It may happen that at the base of the cliff the earlier 

 sandstone beds can be found. Now in the cliff alone 

 evidently the limestone is younger than the immediately 

 underlying sandstone. This underlying sandstone may be 

 lithologically identical with that at B, since they come 

 from the same source, and may even contain similar 



