CATARACT FORMATION '279 



to an error made by Hall previous to 1852^ and perpetuated by every 

 geologist since working in Ontario. Even though at that time the 

 writer collected Dcedalus archimedes and Arthrophycus alleghaniense at 

 Grimsby in this so-called Clinton, he noted that these fossils had two 

 occurrences — one in Medina, the other in the Clinton of Ontario ; but it 

 was not until the summer of 1912, while geologizing in the Georgian Bay 

 region of Ontario with Dr. Merton Y. Williams, of the Geological Survey 

 of Canada, that the error became apparent. Here in the northwest lime- 

 stones predominate, and these had also been regarded as of Clinton age; 

 but there is here an abundance of Cmlospira planoconvexa, Bhinopora 

 ven-ucosa, and Helopora fi'agilis, forms of the "Clinton" of Hamilton, 

 with none of the guides characterizing the Clinton fauna as developed 

 between Niagara Falls and Rochester. The former fauna rested either 

 on the abundantly fossiliferous Richmond or on the Queenston red shales. 

 This superposition at once raised the question, What has become of the 

 Medina ? 



Later in the same season, while in the Georgian Bay-Manitoulin coun- 

 try, the writer was so fortunate as to meet in the field Prof. William A. 

 Parks, and to him our difficulties were related. Together we decided to 

 restudy the sections at Hamilton and Grimsby, and from such a study it 

 soon became plain that the Ontario "Clinton" not only underlay a vanish- 

 ing remnant of the true Clinton with Pentamerus ohlongus, but, what 

 surprised us more, the fossiliferous Medina was also above these beds, 

 though greatly thinned. Professor Parks then told the writer of the 

 well exposed section at the cataract of the Credit River, where there is 

 not a trace of the Medina, and after two clays spent here it was decided 

 to make this the typical, section for the new Cataract formation. The 

 writer, however, then held that the Cataract underlay the Medina, and 

 that these formations were not the equivalents of each other. These oc- 

 currences were announced before the Paleontological Society at its New 

 Haven meeting, in December, 1912, and the results and the name Cataract 

 formation were later accepted in Guide Book Number 5, prepared by 

 Parks for the Twelfth International Geological Congress and issued by 

 the Geological Survey of Canada in 1913. 



The Cataract formation is typically developed along the forks of the 

 Credit River, and is especially well exposed at the cataract, as has been 

 said. Here the formation has a thickness of about 106 feet. This is the 

 average development, though in the various sections the formation varies 

 between 54 feet (Niagara) and 126 feet (Manitoulin). To the south- 

 east, toward Niagara River, the formation becomes more muddy and 



« Pal. N. Y„ vol. ii, 1852. 



