williams] THE EQUIVALENCY OF THE CHAPMAN FAUNA. 87 
In addition to the above, Ilomalonotics hnightii Konig is reported 
from the Upper Ludlow, and also from Zone D, Arisaig'; and an unde- 
termined representative of the same genus appears among the Chap- 
man specimens. 
The presence of plants is further significant. In the Chapman 
sandstone a specimen of Psilophyton, which is probably P. princeps, 
appears in the midst of the marine fossils, giving evidence of prox- 
imity of land, and also of the transition condition leading up to the 
Old Red sandstone type of Devonian. "Psilophyton (?)" is also re- 
ported from the Upper Arisaig, 1 and it is the "Tilestone" of Wales 
(= Upper Ludlow and Downton sandstone) in which the earliest 
known traces of land plants appear in the Welsh succession. 2 
The above evidence leads directly to the conclusion that the fauna 
of the Chapman sandstone of Maine is the equivalent of the Tilestone 
fauna of Wales and of the uppermost Arisaig fauna of Nova Scotia. 
The latter has alread}^ been authentically identified with the "Ludlow 
Tilestone" by Salter, and the general fauna of the Upper Arisaig has 
been identified with the Lower Helderberg by all those who have 
studied the species. 
The Nictaux iron-ore fossils indicate a somewhat younger fauna, 
which has been recognized by Dawson and other paleontologists as 
approximately equivalent to the Oriskany sandstone of the New York 
section. 
In the Gaspe series the place of transition from the Gaspe lime- 
stones to the sandstones is very near to the horizon of the Oriskany 
sandstone farther west. The stratigraphic and petrographic evidence 
in the Maine series points to the equivalency of the Chapman sand- 
stone with the base of the Gaspe sandstone. The particular fauna of 
the Chapman sandstone is not known, at present, in the Gaspe series. 
But if this correlation with the Gaspe series be correct, the relations 
of the several known faunas of the Maine series are in complete har- 
mony with the known succession of the Gaspe faunas, and with such 
an interpretation. In that case the Square Lake fauna of Maine 
would be equivalent to the fauna of the upper limestones in the Gaspe 
limestone series, and thus correspond with the known sequence of 
faunas in the Arisaig series. 
Reviewing the whole evidence, the Chapman fauna must be regarded 
as the equivalent of the topmost fauna of the typical Welch Silurian 
system ( = Upper Ludlow, Tilestone of Murchison, or Downton and 
Ledbury formations of later authors). This places the Silurian -Devo- 
nian boundary for North America where it was determined to be by 
De Verneuil in 1847, 3 classifying the Lower Helderberg formation 
iAmi, Catalogue of Silurian fossils from Arisaig, Nova Scotia : Nova Scotia Inst. Sci., 2d series, Vol. 
I, 1892, p. 185. 
2 U. B. Woodward, The Geology of England and Wales, 1887, pp. 104, 105. 
3 Note sur le parallelisme des depots paleozoiques de l'Amerique septentrionale avec ceux de 
l'Europe: Bull. Soc. geol. de France, 2d scries, Vol. IV. 
