Page:The Habitat of the Eurypterida.djvu/109



It is thus seen that there are 41 feet 7 inches between the Lockport dolomites and the Vernon red shales, although there are two initial red beds, Nos. 7 and 3, showing that the red shale sedimentation was already in progress. A comparison of the two sections shows that the first bed of red shale (No. 7) comes at from 2 to 5 feet above the upper eurypterid-bearing bed, while the lower eurypterid bed (No. 10) occurs 21 feet above the typical Lockport-Guelph. In the lower interval are several thin beds of dolomite, and a waterlime showing sun-cracks occurs. The two shale beds are separated by a dolomite bed 10 inches thick, and in the lower black shale is a dolomite parting $$\tfrac{1}{2}$$ to 1 inch thick. The thin dolomite beds are often sun-cracked, indicating temporary exposure during formation.

The formations indicate a progressive change of conditions from those of Niagaran (Guelph) time when the widespread Stromatopora reefs were forming and the Guelph fauna flourished, through the period when impure dolomites were deposited in thin, ripple-marked layers containing some marine organisms and "fucoids," followed by conditions favorable to the formation of the impure bituminous limestone, to the final stage of the deposition of the impure porous limestone, 2 feet in thickness and containing a branching organism thought by