158 THE CANADIAN NATURALIST. [Yol. viL. 



coralline limestone. The rock was nevertheless marked by the 

 characteristic fossils, and its place in the series clearly preserved.. 

 Eeturniug to the Xianara river, the speaker traced upon the map 

 the course of the Niayfara "roup chrouuh Ontario to Cabot's 

 ilead, thence by the islands of Lake Huron and the peninsula 

 between Green Bav and Lake Michigan, and thence alono- the 

 west shore of that lake to its southern extremitv ; from this 

 point the formation e.xte.nds in a westerly and north-westerly 

 direction through Illinois and Wisconsin, and thence int^ Iowa. 



Returninii' thence to the western end of Lake Erie, the Niagara 

 formation was found composing some islands, and extending- 

 south-westerly into the State of Ohio and into Kentucky. Over 

 all this area the formation is well defined, and no one had ques- 

 tioned its character. The same formation was also known ia 

 Southern Illinois and Missouri, and likewise in Tennessee, where 

 its integrity has been called in question. In Illinois and Ten- 

 nessee it was claimed that the fossils of the Niagara formation 

 are mingled with those of the Lower Helderberg group. He 

 then proceeded to speak of the rocks of this group as known in. 

 its best developments, in the Helderberg Mountains and on the 

 banks of the Schoharie and Cobles Kil. The members of the 

 formation are the Tentacalite limestone, the Lower Pentamerus 

 limestone, the shalylimestone. and the Upper Pentamerus lime- 

 stone, these together constituting a group quite unlike the Niag- 

 ara group, while of the hundreds of fossils which they contain 

 none are identical with those of the Niagara. These beds in the 

 Schoharie Valley lie above the coralline limestone, which has 

 been shown to be a continuation of the Niagara formation and to- 

 be separated from that by a distinct formation known as the 

 water-lime. 



On tracing this Lower Helderberg formation on the map, it 

 was shown to thin out in its westerly extension until it was re- 

 cognized only MS a simple band of. limestone without fossils. 

 Here, returning to the Helderberg Mountains, the formation 

 could be traced to the Hudson River Va-1 ley, and alons: this val- 

 ley to the southern part of the State, thence through New-Jersey, 

 Pennsylvania, Maryland, Virginia, and, thence into Tennessee. 

 Throughout the greater part of this extent the fortnation is 

 underlaid by the water-lime formation, and the purity and iden- 

 tity of the formation has not been questioned. Looking to the 

 north-east, the formation is known as lying unconformably over 



