126 Canadian Record of Science. 



the lithological types, and each of these bands will be 

 composed of beds and each bed may contain forms suc- 

 cessively older or younger than the beds of the same zonal 

 band above and below. When there has been (more or less) 

 continuous depression of the land for a long interval, with 

 (more or less) continuous supply of material suitable for 

 all three zones, then subsequent uplift and erosion over 

 extensive areas, the formation resting upon the oldland 

 surface will normally be a sandstone. The earlier formed 

 portion of this sandstone will naturally carry fossil forms 

 appropriate to the age in which they lived, and the later 

 formed likewise. Ami has recently drawn attention to 

 arenaceous character of the formations resting upon the 

 older rocks, along the axis of the Appalachian system, 

 and to the progressive change in faunas from Cambrian 

 types in New Jersey northward to Ordovician types in 

 Canada, as illustrating the progressive depression of the 

 land areas during the progress of early palaeozoic time. 1 



Further, it must be noted that, although the normal 

 type of deposits would show the threefold lithological 

 grouping, yet irregularities in the supply of material and 

 variations in the character of that which is supplied, 

 variations which will be of very frequent occurrence, will 

 mean that in the field truly contemporaneous beds in the 

 three zones will be rare, that all three types of deposit may 

 be composed of the same kinds of material, a feature 

 frequently seen in the limestone deposits, and, thirdly, 

 that one or more of the types may be completely wanting. 



After a long interval of time during which a succession 

 of deposits has been formed under varying conditions, the 

 sea bottom becomes uplifted, and the new formed rocks 

 are subjected to long continued disintegration, degrada- 

 tion, and dissection. The greater part of the deposits are 

 worn away ; fragments only remain here and there, 

 scattered over the area where they were once continuous, 



1 Ami, Geo. Soc. Amer., Winter meeting "1903-03. "The Eparcbean Formation." 

 s ee Bull., G.S.A., Vol. 14. 



