308 C. SCHUCHERT MEDINA AND CATAEACT FORMATIONS 



Niagara Gorge, Neiu Yorlc-Oiiiarlo, section (20 miles west of Lode- 

 port ). — Along line of ISTew York Central Railroad and Grand Gorge 

 Trolley. See Grabau, Bulletin 45, New York State Museum, 1901, pages 

 87-95, and Kindle and Taylor, Geologic Folio 190, U. S. Geological Sur- 

 vey, 1913. 



Lockport dolomite. Thickness about 150 feet. 



The main upper mass of about 120 feet is a dark bluish gray to brownish 

 colored, thin-aud thick-bedded, more or less coarsely crystalline dolo- 

 mite that is somewhat petroliferous and with geode cavities contain- 

 ing gypsum, selenite, dog-toothed spar, etc. In the highest beds are 

 the precursors of the Guelph fauna, here always rare in species (see 

 Clarke and Ruedemann, Mem. 5, N. Y. State Mus., 1903). The fos- 

 sils include Coelidium macrospira, Pterinea sulyplana, Phragmoceras 

 parvum, etc. Otherwise the fauna is largely a modified Rochester 

 assemblage. 

 Oasport memher (Kindle, 1913). "Crinoidal limestone" or marble. Usu- 

 ally a non-magnesian limestone, but may also be transformed into a 

 dolomite; replete with crinoidal fragments and local diagenetically 

 changed Bryozoa reefs. From 7 to 20 feet thick. Fauna essentially 

 that of the Rochester, with Callicrinus, Ichthyocrinus conoideus, 

 Eucalyptocrinus tul)erculatus, etc. 

 DeCew memher. Drab to bluish gray, fiue-grained, impure limestone or 

 cement rock, that iu the upper 3.5 feet is more or less strongly wave- 

 worked, 6 to 9.5 feet thick. This horizon is in many places marked 

 by irregular contacts, both above and below, and by the lithic differ- 

 ences between the aujacent formations. The upper contact is very 

 regular, but the lower one is here decidedly irregular. No fossils. 

 In some ways this member seems to be a transition zone under dis- 

 turbed conditions from a shallow muddy sea to deeper limestone- 

 making waters. 



IrreguJar u-avy (? eroded) contact. Time break, if any, short. [Grabau as 



'^nsor questions the broken contact here. It becomes, according to 



je writer, more and more prominent to the northwest. The former 



states that it is another case of lateral change in the sedimentation.] 



Rochester shale. About 60 feet thick. 



The upper part of this formation has many thin layers of limestone re- 

 plete with many species of Bryozoa described by Bassler (Bull. 292, 

 U. S. Geol. Surv., 1906). The fauna gradually vanishes upward and 

 in the uppermost beds there are almost no fossils. 

 The lower portion is all shale and is rich in fossils, especially toward the 

 base. It has been described by Hall (Pal. N. Y., II, 1852) and is in 

 the main derived from about Lockport. Much of this fauna appears 

 in the Clinton below (Irondequoit). The more characteristic common 

 fossils are Caryocrinns ornatus, Stephanocrinus angulatus, Eucalyp- 

 tocrinus cwlatus, Thysanocrinus liliiformis, Lyriocrinus dactylus, Ich- 

 thyocrinus Iwvis, Dictyonella corallifera, Anastrophia interplicata, 

 Rhynchotreta americana, Spirifer niagarensis, Trematospira camura, 



