334 



Report of the State Geologist. 



went on in the Genesee Valley, allowing there the luxuriant development of 

 the faunas which had flourished earlier in the more western waters, and 

 which had migrated to their new station when the conditions became uni- 

 form. At Eighteen-mile creek, however, subsidence had practically ceased, 

 and thus, while 280 feet of calcareous mud accumulated above the Encrinal 

 limestone in the Genesee Valley, only seventeen feet accumulated in the 

 vicinity of Eighteen-mile creek. The shoaling of the waters in the Eighteen- 

 mile creek region was the means of driving out the last survivors of the 

 Lower (Spirifer mucronatus) and the Encrinal limestone (S. sculptilis) faunas, 

 which found their normal environment farther east, in the subsiding Genesee 

 Valley trough. While the lower Moscow, or S. consobrinus fauna existed at 

 Eighteen-mile creek, the conditions about Widder, Ontario, were very similar, 

 as proved by the similarity of the fauna. But in this latter region subsidence 

 continued, allowing the uninterrupted existence of this fauna, while at 

 Eighteen-mile creek owing to the continued shoaling of the water, it soon 

 became extinct. That the shoaling of the water was at first a comparatively 

 rapid one, seems to be indicated by the sudden overwhelming of the coral 

 forest which had grown for some time after the Encrinal limestone bed had 

 been formed. As already pointed out these corals lie piled one upon the 

 other often three or four deep, and scarcely a single one remained standing. 

 To the wave action in this region, and probably also to the maceration result- 

 ing from long exposure before burial, must be attributed the loss of the spines 

 in most of the specimens of Atrypa aspera, only a very small number pre- 

 serving any trace of them, while in the Genesee Valley almost every specimen 

 ■shows them. The smooth water-worn pebble and the water-worn fragment 

 of a Spirifer granulosus found in the lower Moscow of Eighteen-mile creek, 

 while in themselves of little value are of interest in connection with the other 

 proofs of shallow water in this region. S. granulosus as noted above does 

 not occur in the Moscow shales of Eighteen-mile creek, but is abundant in the 

 Encrinal of that region. The shale itself bears evidence of having accumu- 

 lated in shallow water, by the presence of plant remains, and by its lithologic 

 character. 



The reversal of conditions is also shown by the occurrence in the 

 lower Moscow of Eighteen-mile creek, at about a foot above the Encrinal 

 limestone, of a bed composed almost entirely of Ambocodia umbonata and 

 by the occurrence at Livonia of a similar bed twelve feet below the Encrinal 

 band. Similarly bands composed of lAorhynchus multicostiis occur in the 

 Lower shale at Livonia, and in the upper part of the Upper shales at Eight- 



