Williams] THE SILURIAN-DEVONIAN TRANSITION. 25 
cation of any rocks or faunas to be correlated with the Onondaga or 
Guelph, is confirmed, by the Maine series of faunas and formations. As 
far west as St. Helens Island, Lake Meniphremagog, and Dudswell, in 
Quebec Province, where the Silurian is recognized by occasional fos- 
siliferous rocks, everything at present reported points to a geologic 
history in common with the Anticosti and Gaspe regions, and not in 
conformity with the events recorded west and south of Hudson River. 
In classifying the Maine faunas, closer correlation is to be expected 
with the faunas of the eastern province than with the Appalachian or 
interior provinces. Not only do the Maine faunas agree in general 
sequence and composition with those of this eastern province, but this 
fact is of great significance in correlating American with European 
systems. 
The boundary between the Silurian and Devonian systems was first 
made in the Welsh series, in which the transition was from calcareous 
sedimentation, with rich and purely marine faunas, into sandstones of 
great thickness containing land plants and fishes whose habitat was, 
presumably, fresh or brackish waters. 
The New York section, from the Lower Helderberg limestones 
through the Oriskany, Cauda-galli, and Schoharie grits back again into 
limestones, does not pass out of marine conditions. In the Gaspe 
region, however, there is a complete change (as there was on the other 
side of the Atlantic Basin) at the point where the Oriskany fauna was 
evolved. In these Silurian faunas of the eastern province there is 
also much closer resemblance to the Wenlock-Ludlow series than is 
found in the faunas of the Appalachian province in New York. The 
correlation of the passage beds at the top of the Silurian of Wales is 
clearly to be recognized in the passage from the Gaspe limestones to the 
Gaspe sandstones of the eastern province of America. This Gaspe 
transition is also to be traced with precision to the horizon of the intro- 
duction of the Oriskany fauna into the basins farther west and 
southwest, in which no direct passage into Old Red sandstone condition 
is apparent. 
We have thus in America a means of determining where the Silu- 
rian boundary belongs in purely marine series of beds and among 
marine faunas of unbroken succession, The Lower Helderberg in the 
interior of the American continent, as the Koniprusien F2 fauna in 
the Bohemian Basin of Europe, is closely related in its species to what 
succeeds', because there was no radical disturbance of the conditions of 
marine life. Nevertheless, it is not the Lower Helderberg species 
that mark the conditions corresponding to th? beginning of the Old 
Red sandstone; but the changes which that fauna suffered during the 
passage into the Oriskany time are evidences of a general disturbance 
which resulted in the lifting of large areas of marine surface above the 
level of the sea. 
