170 THE CANADIAN NATURALIST. I Vol. 



IX. 



We may have difficulties in fossils as well. Nothing is more 

 common than to find in the modern ocean areas traversed by 

 cold currents which have very different animals living in them 

 from those in the same latitude where the water is warmer. The 

 same thino; occurs in older formations. The abundant corals and 

 larii'e shell- fishes in our Montreal limestone of the Trenton aoe, 

 show a condition of thiuo's in which the ureat area of Central 

 North America was covered with warm waters from the south, 

 teeming with life, and was sheltered from the northern currents 

 of cold and muddy water. But in the Utica shale which suc- 

 ceeds, we have the effect of these cold currents flow^ing over the 

 same area, loading it with mud, over which lived Graptolites 

 and old fashioned northern Trilobites like Triarthru.s Bcckii, 

 instead of the rich life of the Trenton. This is a mere chansjje to 

 a cold or glacial age. 



Now when I inform you that all these causes of error em- 

 barrass the study of the Quebec group of Sir William Jjogan, 

 you will be able to appreciate the difficulties of the case. 

 Crossing the narrow line, a mere crack of the earths crust, the 

 great reversed fault of Eastern Canada and Lake Champiain, we 

 pass at once from the flat uniform deposits of the great conti- 

 nental plateau of America to entirely different beds, formed at the 

 same time alon<2- its Atlantic margin. These beds were affected 

 by volcanic ejections mixing them with ash rocks and causing 

 huge earthquake waves, which tore up the rocks of the sea- 

 bottoms and coasts, and formed great irregular beds of conglome- 

 rate, sometimes with boulders many feet in length. In the 

 intervals of these eruptions the area was overflowed by cold 

 Arctic currents carrying sand a)id mud, sometimes altogether 

 barren of fossils, or again loaded w^ith cold-water creatures like 

 the Graptolites, which occur in vast quantities in some of the 

 beds. Alternating with all this were a few rare lucid intervals, 

 when fossiliferous limestones, just sufficiently like those of the 

 great interior plateau to enable us to guess their similar age, 

 were being produced here and there. Farther, this heap of most 

 irregular and peculiar deposits was that along which subsequent 

 flexures and igneous eruptions and alterations of beds both by 

 heat and heated waters were most rife, all the way down to the 

 Devonian period. 



At first the real conditions of this problem were hidden from 

 Sir William Logan, by the error of supposing, with most of the 



