Grabau — Faunas of the Hamilton Group. 



335 



een-mile creek. These two species evidently could thrive in the shallow 

 muddy waters. While the Hamilton conditions continued for a long time in 

 the subsiding Genesee Valley trough, the Genesee conditions appeared in the 

 Eighteen-mile creek region as shown by the occurrence in the barren middle 

 " Moscow " of the Orbiculoidea media band with Sehizobolus truncatus. This 

 latter species also occurred during the existence in this region of the S. tullius 

 fauna, and in the transition beds above, it becomes very prominent. That the 

 Styliolina limestone was accumulated in comparatively shallow water, and 

 does not indicate a great subsidence seems to be shown by the annilid jaws of 

 the Conodont bed immediately underneath it ; for these animals probably 

 never live in water of any great depth. The more or less broken and frag- 

 mentary fish plates and scales may indicate the same thing. 



During all this time the deposition of black shales in the southern and 

 western states continued uninterruptedly, these according to H. S. Williams,* 

 representing the Marcellus, Genesee, and Ithaca shales. 



CONCLUSION. 



If any general conclusion is to be drawn from the foregoing discussions 

 it- is that in every locality the development of the faunas at any horizon 

 depend largely upon local conditions, and a fauna which may characterize one 

 part of a group at one locality, may characterize a different portion of the 

 same group at another locality, and that consequently close correlations can 

 not be made, without taking all the local factors into consideration. 



While this makes of stratigraphy a vastly more difficult and intricate 

 subject, it also greatly enhances the value and interest which it possesses, 

 when regarded from a purely scientific point of view. 



♦Proc. A. A. A. S. vol, 30. p. 1S6. 



