118 Canadian Record of Science. 



6. The uniform Rate of Depression may be less than 

 the Eate of Supply of Detritus which is variable. 



The remaining six relationships, when the Rate of 

 Depression is not uniform but variable, may also be 

 tabulated in a similar way ; or all twelve relationships 

 may be indicated graphically, thus : — 



Rate 



of 



Depression. 



Uniform > Uniform 



> 



Variable = 

 < 



Rate 



of 



Supply 



of 



Detritus. 



When there is uniform rate of depression and uniform 

 rate of supply of detritus, the rate of the latter being less 

 than the rate of depression, the seaward zones will 

 gradually encroach upon the shoreward zones, the 

 materials of the shale and sand zones will become com- 

 mingled, and it may even happen that the limestone will be 

 deposited directly upon what was the oldland surface. In 

 this latter event the lower beds would be apt to become 

 caleareous grits or conglomerates. Such conditions seem 

 to have existed at one time in the vicinity of Kingston 

 Mills, Ontario, where a calcareous conglomerate of Black 

 River age, carrying angular quartz fragments, casts of a 

 Cameroceas, and fragments of crinoid stems is found rest- 

 ing directly upon an Archean red granite. 1 Similar con- 

 ditions seem to have existed in the Hudson Bay Basin 

 during a portion of Devonian time. Parks describes the 

 occurrence of certain Devonian corals in the basin of the 

 Moose River with their bases attached to an Archean 

 boss. 2 In the instance cited the boss of Laurentian gneiss 

 probably formed an island in the Devonian sea at some 

 distance from the shore of the oldland. The rate of 

 depression was slow enough for the formation of a sand- 

 stone conglomerate near the shore. 



1 Wilson, Phys. Geol., Central Ontario, Can Inst., Trans., vol. VII., p. 148. 



2 Parks in Iieport of the Bureau of Mines, Ontario, 1899, p. 188. 



