312 C. SCHUCHERT MEDINA A^B CATARACT FORMATIONS 



Disconformity. Contact sharp between adjacent beds. About 40 feet of 

 Rochester is absent. 



Rochester shale. Thickness about 25 feet. 



Hard dark blue shales alternating with thin limestone bands, many of 

 which are replete with bryozoans and some brachiopods. The con- 

 tact with the Clinton is also sharp, but no break in sedimentation is 

 recorded. 



Clinton limestone. Thiekhess about 14 feet. 



Irondequoit limestone member, in a single bed 4.-5 feet thick. 

 Wolcott limestone memher. The thin-bedded Clinton in sharp contact 

 with the Medina below. Thickness about 9 feet. The basal 2 to 8 

 inches of the Clinton is a clean-washed sandstone with occasional 

 small pebbles of a greenish sandstone, both derived from the Medina. 

 As usual, 18 inches above the base Pentamerus ohlongus (Clinton 

 form) is common. 



Disconformity. The evenly bedded Clinton limestone on the decidedly cross- 

 bedded sandstones of the Medina makes a sharp and broken contact. 



Medina sandstone. Thickness about 18 feet. 



Light green, thin-bedded, decidedly cross-bedded, clean-washed sandstones, 



with a thickness of about 7 feet. 

 Variegated, green and red, thin-bedded sandstones, with a thickness of 

 about 10 feet. Near the middle of this zone occur mud-ball forma- 

 tions (sea-churning) like those seen in the Medina of the Niagara 

 Falls Gorge. 

 Light green sandstone and shale in thin alternating beds with a total 

 thickness of about 1 foot (basal sandstone 1.5, shale 2, sandstone 2, 

 and shale and thin sandstones 4 inches). Marked by an abundance 

 of Scolithus verticalis burrows. On the imder side of the lowest 

 sandstone occur rarely Helopora and undescribed bivalves, forms 

 that also occur below in the Cataract. 



Cataract formation. Thickness about 90 feet. Exposure complete. 



Ca'bots Head shale meml)er. Upper red and green sandy shales with 

 bands of impure magnesian limestones having a thickness of about 22 

 feet. Toward the top the formation becomes more and more sandy 

 and in the uppermost 5 feet has intraformational conglomerates, the 

 pebbles of which are small. At 3 to 5 feet below the Medina occur 

 abundantly Helopora fragilis, lAngula clintoni and undescribed bi- 

 valves. These occurrences prove that there is no break here between 

 the Cataract and the Medina. 

 Lower olive green shales (decidedly so in upper half) with many thin 

 layers of magnesian limestone that become more abundant down- 

 ward and are replete with fossils. Total thickness 48 feet. Rhin- 

 opora verrucosa and Cdclospira planoconvexa appear 10 feet above the 

 Whirlpool sandstone. Twenty-five feet higher occurs an abundance of 

 large Whitfieldella near ohlata. 

 Manitoulin limestone member. Basal magnesian limestones, 8 feet thick. 

 Whirlpool sandstone memher, 12 feet thick. The upper 3 feet or more 

 are thin-bedded, greenish, shaly sandstones, more or less cross-bedded. 

 Below, the sandstone is regularly and heavy bedded, greenish white 

 in color, and may or may not be blotched with red. The basal 1 or 2 



