1888 .] 
35 
[Hitchcock. 
lication. It so happens that we have defined this belt of rock very 
differently. Let that definition be accepted which proves to be the 
more correct. The Georgia group was proposed by me to embrace 
two other terranes as well as the one under consideration, and the 
name of Georgia was employed because the whole group was ex- 
hibited within the township with characteristic fossils, and its use 
did not commit the report to any one of the three views that had 
been proposed for its age. Its precise place was left to the final 
decision, as awarded by paleontologists, of the value of the fos- 
sils. My definition embraced three points : (1) it rested upon the 
red dolomitic sandrock ; (2) it was 3000 feet thick and much more 
in the southern terrane ; (3) it extended eastward across the rail- 
road and constituted the slates at St. Albans village, the eastern 
portion being the newest. On the west, it joined the Hudson river 
slates, and the place of the supposed fault plane was indicated, but 
its existence was neither affirmed nor denied. Mr. Marcou’s Geor- 
gia slate (1) underlaid the red rock [Potsdam sandstone] uncon- 
formably, (2) was from 500 to 600 feet thick, (3) the rocks to the 
east of Georgia center belonged to an older series 2500 to 3000 feet 
thick, called the St. Albans group, because the village of that name 
rested upon it. Thus this definition includes only a sixth part of 
the strata called by this name in the Vermont report. Nothing 
was said of the slates to the west of the red rock in the November 
communication, but in a later publication they are referred to the 
Upper Taconic. 
An exhaustive survey of this region has recently been made by 
C. D. Walcott and published in the Bulletins of the U. S. Geolog- 
ical Survey, Vol. iv, No. 30, 1886. No geologist is better qualified 
than he to settle these questions which we are discussing, espe- 
cially as he has studied a wider field than either of the dispu- 
tants. The southern terrane referred in the Vermont report to the 
Georgia group is referred to the same horizon by Walcott in a later 
publication. Concerning the rocks under discussion he (1) makes 
the slates to overlie the red rock, and adds that to the Georgia 
group, as was done by Logan before him, who used the name of 
Potsdam ; (2) The thickness is nearly 9000 feet; (3) the eastern 
continuation is to the same line, the eastern part being the highest. 
The slates west of the red rock are separated from it by the great 
fault and they are of Hudson, river age. The so called St. Albans 
group of Marcou is not mentioned by name, but its strata are made 
