102 The American Geologist. August, 1903. 
Whether this southern subsidence reopened communication 
with any southern ocean it is not at present possible to deter- 
mine. Xor is it absolutely certain that in some* places a part of 
this black shale may not represent a rather earlier time. But 
the evidence of the fossils, so far as it exists, indicates that the 
shale marks the closing stages of Devonia in eastern North 
America. 
Adopting the above stated view, the history of the period 
then will be on this wise. Continued elevation in the northeast 
produced continued erosion and removal of sediment. Con- 
tinued depression in the Appalachian gulf provided room for 
this sediment, the coarser portions of which were dropped near 
the shore and in the northeastern estuary, while the finer parts 
were carried farther out to sea and only subsided after a voy- 
age of several hundred miles. Accordingly, we must regard 
the Oneonta sandstone and the sandy and conglomerate ex- 
tensions of the Chemung and the following massive Catskill 
as the shore and estuarine deposits in the gulf, while the black 
and other shales beyond the shore-sands constitute the off- 
shore strata and grow finer and less abundant in direct pro- 
portion to their distance from land. 
The proportion of sand continued and even increased after 
the Catskill period had come to its end. The most obvious and 
rational explanation of this fact is that the northeastern uplift 
became more rapid and the erosion therefore more severe as 
time passed on. One step further into the region of speculation 
would suggest that Xew England and the rest of the elevated 
area were formerly covered, in whole or great part, with such 
deposits as those which elsewhere composed the bottom of the 
Appalachian sea, namely : the Trenton limestone and the Utica 
and Hudson river shales, whose destruction supplied for a long 
time little besides soft material to the eroding waters. But 
when these had been removed and the harder underlying strata 
had been exposed, such as those of which the region today con- 
sists, the supply of fine material gave place to one of sand or 
even, at times, to pebbles, thus causing the gradual, but dis- 
tinct, change so note-worthy in the strata. 
Again, a singular change in the fauna lends no little sup- 
port to the above interpretation of the facts. The lower Che- 
mung has an abundant fauna which gradually disappears up- 
