316 J. D. Dana on American Geological History. 
with this deposit the Upper Silurian began. 
The U Siluri 
reef, far exceeding in extent, if not in brilliancy, any modern 
coral sea; for such was a portion, at least, of the Upper HEL- 
DERBERG Period. 
Again there was a general devastation, leaving not a trace of 
the former life in the wide seas; and where were coral reefs, eS- 
pecially in the more eastern portion of the continental seas, 
sandstones and shales accumulated for thousands of feet in thick- 
ness, with rarely a thin layer of limestone. Thus passed the 
HAMILTON, CHEMUNG and CaTsKILL Periods, of the Devonian 
age. The life of these regions, which in some epochs was eX 
* Prof. Hall, in connection with J. D. Whitney, has recently made the important 
observation, that the Galena or lead-bearing limestone, which is the upper 
rent is ' fro: Ni i 
se 
sin by thick strata of Hudson River shales, giving a rolongation to these shales 
Whi n ese 
before unsuspected. He had previously, with Mr. 
around the north side of Lake Rutod an 
thence along Green Bay to Lake Winnebago, These shales are however partly re- 
placed by limestone in Ohio, ete. 
ee ee ee 
an exuberant coral _ 
d Lake Michigan to Pointe aux Baies, and ag 
