SILUEIC CORAL REEFS 343 



quariy the rocks are all composed of coral, shell, or crinoid sand, and 

 are locally known as sandstones. Fossils are rare, those found being 

 chiefl}^ brachiopods or crinoid fragments, with an occasional cephalopod 

 shell. The succession of bedded strata is as follows : 



3. Porous vermicular dolomite, brittle and with stratification poorly devel- 

 oped, full of cavities of dissolved corals about. . 20 feet 



2. Hard white granular lime rock about. . 8 feet 



1. Soft friable brown lime sandstone. 10 feet 



Total about.. 38 feet 



Anschiitz's quarr}^ in Cedarburg, is opened in a hill, near the center 

 of which, south of the quarr3^ occurs a reef, as indicated by the nature 

 and dip of the strata. The dip is 10 degrees northeastward. The lime- 

 stones of this quarry are all well bedded and uniform, sugary in texture 

 and with few fossils. Those found are chiefly brachiopods. The rock 

 here has the structure of a sandstone, by which name it is familiarly 

 known. Other quarries and natural exposures on the Milwaukee river 

 near Grafton show similar bedded limestones, but no other exposures 

 of reefs were found. 



SILURIC CORAL REEFS OF GOTLAND 



Dr Carl Wiman has described ^ the characteristics of a certain type 

 of' Klintar " of the northwest coast of the island of Gotland as repre- 

 senting reef masses of the Siluric formations of that region. These com- 

 pact reef masses have resisted erosion more readily than the connecting 

 beds of stratified material, and hence they form a succession of promi- 

 nent headlands where they have come within the zone of wave activit}^ 

 on that coast. The main mass of the reefs is unstratified, or at best the 

 bedding is but slightly developed. In form the}^ are lens-like, and they 

 consist chiefly of masses of coral, stromatoporoids, and bryozoa, which 

 have grown in sitii, together with calcareous algae. Between these, 

 remains of brachiopods and crinoids are abundant. On the flanks of 

 the reefs are found conglomerates and breccias of coral masses, such as 

 Halysites and Cystiphyllum, and crinoidal remains. The coral heads of 

 the margin of the reef are often overturned, while farther away they are 

 most generall}^ fragmentary. Along the margin of the reef, furthermore, 

 there is a periodic overlapping of the fragmental and organic rock, as 

 has been noted for the reefs previously described. Even within the 

 reefs occur small wedges of sedimentary beds, while beds not infrequently 

 suddenl}^ thicken on reaching the reef, a feature already noted, as found 

 by Chamberlin in the Siluric reefs of Wisconsin. Similarl}^, we meet 



* Uber Silurisohe Korallenriffe in Gotland. Bull. Geol. Instit. of Upsala, vol. iii, 1897, pt. 2. 



