284 NEW YORK STATE MUSEUM 



inaugurated all about the Adirondacks causing the interior 

 sea to spread northward and eastward over the entire region. 

 The Black Kiver is locally absent along some of the southwest 

 border, owing to slight irregularities in the floor on which it 

 was laid down, and less frequently some of the basal Trenton 

 is absent from the same cause. Whether these irregularities 

 were due to wear or to slight folding has not been determined. 



While apparently some slight remnants of the old Adirondack 

 island persisted above sea-level during the whole or part of the 

 Trenton, it is probable that they were of insignificant extent and 

 likely confined to the southern part of the region. With these 

 possible exceptions the sea of the closing Trenton seems to have 

 overswept the entire Adirondack region. 



The Black River and Lower Trenton are quite pure limestone 

 deposits and hence clear water formations. But the Trenton 

 soon comes to show some mud admixture, at first slight and inter- 

 mittent but slowly increasing in amount, till finally it equals 

 and then exceeds the lime, and the deposit becomes a calcareous 

 shale rather than a limestone. These muds came from some 

 land area to the eastward and progressively invaded the sea 

 toward the west, so that limestone was still in progress of forma- 

 tion on the west while shales were forming to the east. 



XJtica formation. The limestones of the Trenton pass gradually 

 upward into shales through increasing invasion of mud from the 

 east. Trenton submergence was much interrupted on the south 

 and southeast, so that the formation is much thinner there than 

 on the west and the northeast. In the latter locality the greater 

 thickness is likely due to more rapid, or to less interrupted sub- 

 sidence. On the west it is, at least in part, due to the gradual 

 encroachment westward of the muds. Eventually however the 

 conditions of mud deposit held sway over the entire region and 

 far beyond. The sea was not deep, and the muds were swept in 

 by currents moving toward the southwest. Subsidence was con- 

 siderable, so that several hundred feet of shales accumulated in 

 nearly all parts of the region, and in some portions a much greater 

 thickness. 



