I'l'l 'Tin American Geologist. August, 1894 
limit was nol oulj one of a geological series, bul the dead-line of a large 
number of organic types. In the typical Devonian sections, however, 
the lower boundary was never defined, and English geologists to-daj 
concede thai the earliesl members of the Devonian series are absent or 
unexposed in these sections. The Devonian system was founded upon 
imc nt' i ln> nil isi unfavorable and incomplete developments of that series of 
rocks and faunas known in am pari of the globe; a more precise scope 
was given to ii by the work of iis founders, Murchison and Sedgwick, 
in the Rhineland, bu1 even there no detcrminal ion of its lower limii was 
made. This admitted hiatus in the typical succession of Devonian to 
Silurian, is the parent of the prolific discussions over "post-Silurian" 
and "HercYuian" faunas. No such discussions could arise in a counl rj . 
if there be any such, where the interval is filled by a complete succes- 
sion. In America, in particular the state of New York, where the 
Lower Belderberg fauna is typically exhibited, there is an absence of 
physical disturbance in the succession except that indicated by the 
presence of an extensive local accumulation ofgypsum, salt, and water- 
limestone, toward the close of the Silurian, but the meager fauna of 
these beds is followed by the exceedingly prolific one of the Lower Hel- 
derberg, where but wondrous few of the Silurian species appear. There 
may be a Silurian expression in many generic elements in the Lower 
Helderberg, but the entire combination is by no means so early in its 
general expression, or indicative of so close complications with the Si- 
urian, as thai of the Siberian fauna which we have just considered.* 
The early geologists of the state of New York, working out the clas- 
sification of its rocks independently of preconceived notions and alien 
nomenclatures, applied to the formations now embraced under t he terms 
Lower Belderberg. < triskany and Upper Helderberg, the name Helderberg 
division (Mather. Vanuxem), or Helderberg Series (Emmons, Hall): the 
most sharply defined and widely extended geological terrain- in the state. 
There was. indeed, some divergence <>f opinion as to what should con- 
stitute the basal member of this division, Hall and Vanuxem including 
the Onondaga Salt group, Emmons omitting it and beginning the series 
with the Pentamerus limestone. The original definition of the Helder- 
berg division was Mather's and was essentially based upon determina- 
tions made by John Gebhard, jr.. in the valley of Schoharie creek. This 
limitation of it begins the series at the bottom with, the "Maul ins water 
limestones." and terminates it above with "the Seneca limestone of Mr. 
Hall.'* The approximate accuracy of this lower limit as a line of division 
between the Lower Helderberg and the subjacent formation was after^ 
ward established by Prof. Hall. The continuity of the greal series of 
waterlimes constituting the upper pari of the Salt group and the lower 
pari of the Lower Helderberg, makes a division upon lithological 
grounds somewhat uncertain, but the line is fixed, as shown b\ Hall 
and emphasized h\ comparison with the succession in Greal Britain and 
Russia, at the disappearance of the Eurypterus fauna. 
*For a review of the Lower Helilerh'Ttf fauna with especial reference to its Silurian 
and Devonian elements, see Clarke: The Hercvnian Question, 420" Rept. N. Y. State 
Mas. Nat. Hist., pp. HH-4:!7, 1889. 
