81 



on the coral reef proper in this immediate region.* They did 

 not flourish long however, but were soon overwhelmed and 

 disappeared. Some of them, such as Cystiphvllum and the 

 adaptable Streptelasma continued at intervals for some 

 considerable length of time. Aside from these, however, the 

 Hamilton fossils are not common in the Moscow shales of 

 this region. True, there are some adaptable species, such as 

 Phacops rana, which are to be met with everywhere, but 

 the great majority of species had left this region, migrating, 

 during the uniform conditions of the Encrinal limestone age, 

 probably to the eastward. At any rate, most of them 

 re-appeared in the Upper or Moscow shales in the Genesee 

 valley. In this latter region the shales are also much 

 thicker, aggregating nearly three hundred feet, while in our 

 own vicinity seventeen feet constitute the whole thickness of 

 these shales. t The cause of the slight development of these 

 shales in the region under consideration,' was the compara- 

 tively stationary character of the sea bottom, in other 

 words, the absence of subsidence. The water more-over, 

 was shallow over Erie County, the evidence for which is 

 found in the character of the fossils and in the shale itself, in 

 the plant remains which occur in it, and in a fragment of a 

 water-worn shell and a similarly worn pebble which were 

 found.$ 



Throughout the Moscow time, the water probably con- 

 tinued shallow, and life was scarce. The mud flats were 

 probably never exposed at low tide, but their component 

 material was worked over and over bv the tidal currents, so 

 that no perfect lamination was developed. On a sandy sea 

 floor, such conditions would have formed oscillation ripples, 

 but the fine mud did not admit of such impressions, or if 

 they were formed, their preservation in the shale was an 

 improbability. 



•At Morse Creek, near Athol Springs, Heliophyllum, which among others is here 

 referred to, occurs in the Encrinal limestone. 



fFor a comparison of the Hamilton fattnas of Eighteen Mile Creek with those of 

 the Genesee Valley, see "Faunas of the Hamilton Group, etc." 



JThe shell was a Spirifer granulosus, which does not normally occur in the 

 Moscow shales of this region, but is common in the Encrinal limestone, 



