282 The American Geologist. November, looi. 
REEF STRUCTURES:iN CLINTON AND NIAGARA 
STRATA OF WESTERN NEW YORK 
By Clifton J. Sakle, Rochester, N. Y. 
TLATES XXVII- XXXI. 
At no other point in the Ignited States, exceptino- possibly 
Xiag'ara. the type locahty, is there so fine an opportunity to 
study the Niagara series, as in the lower gorge of the Genesee, 
at Rochester, N. Y. ; and the display of Clinton strata is un- 
equaled. 
A phenomenon which early drew the writer's attention in 
the study of this exposure, is the occurrence in the Clinton 
upper limestone of certain irregularly bedded masses which, 
owing to difl^erential weathering, project beyond the general 
ledge face, being apparently parts of irregular lenses. 
In the various exposures of this horizon, for about a mile 
along the Genesee, upwards of forty examples have been ob- 
served, this number being increased by others found in sewer 
tunnelings in the northern cjuarter of the city. The "west side" 
sewer, made in the winter of 1895-6, afforded, sexenteen 
masses in a distance of seven or eight hundred feet. The 
workmen engaged in this excavation called them boulders 
because of their shape and superior hardness. The latter 
character probably accounts for their prominence on weath- 
ering surfaces. 
Outside of Rochester I have found them along the Clinton 
outcrop as far as Niagara river on the west and Marble (Sec- 
ond) creek, Wayne county, on the east, a distance of about 
one hundred and twenty miles. Over one hundred examples 
have been more or less carefully studied bv the author. They 
are absent from extended areas or may occur isolated, or in 
groups, or so near together as to more or less completel}' coa- 
lesce. At Niagara gorge and imder Lewiston heights, eleven 
examples have been observed, but between this locality and 
Lockport an outcrop twentv miles in length has afiforded but 
four. At Gasport in the bed of the creek nearly a score are 
seen. Tn Monroe county, nearlv everv outcrop affords one or 
more, often twinning, and at Marble creek they form an irreg- 
lar continuous stratum, extending for several rods along the 
bed of the stream, though absent from .^almcMi creek three 
