HAMILTON CEMENT ROCK. 399 



In section 11, town of Granville, a railroad cut just south of the 

 flag station, known as Brown Peer, exhibits a few feet of this forma- 

 tion. The original lithological characters are essentially those already 

 described, but the rock of this locality has been more extensively 

 weathered than that near Washington Street bridge, and presents a 

 buff color, except in the interior of some of the heavier layers, and is 

 also somewhat decomposed in certain portions. This is the typical 

 locality of the Chimseroid fish, Rhynchodus excavatus, previously 

 described, and with it are associated the leading forms of the general 

 list above given, prominent among which are Orthis impressa, 

 Strophodonta demissa, S. perplana, Sperifera pinnata, 8. medialis, 

 Speriferina zigzag, Atrypa reticularis, Palceoneilo constricta, 

 Modiomorpha concentrica, and others. It is stated that in the bed 

 of the Milwaukee river opposite this point, the formation exists in 

 place; but it was not accessible at the time of our investigations. 



In sections 9 and 10 of the same township, occurs the most 

 northwesterly exposure of this formation now known. It occupies 

 the brow of a hill, underlaid by limestone belonging to the Niagara 

 formation. The rock is here a rather soft, granular, buff, impure 

 dolomite, much stained with iron, doubtless due to the decomposition 

 and oxidation of pyrites, originally disseminated through it. Orthis 

 impressa, /Strophodonta demissa, Spirifera pinnata, Atrypa occi- 

 dentalis, and A. reticularis, show the character of the fauna. 



Along the lake shore, on Whitefish Bay, the formation rises 

 slightly above the water level in a very limited exposure. The strata 

 at this point have a firmer texture, but more uneven structure, than 

 at the previously named localities. The lines of deposition and bed- 

 ding are irregular. Angular cavities of moderate size are not unfre- 

 quent, some of which are filled with a semi-fluid, tar-like bitumen. 

 An analysis of this rock by Professor Daniells shows it to have the 

 following composition: 



Carbonate of lime 49.12 



Carbonate of magnesia 38 . 76 



Sulphate of lime ..: 0-07 



Phosphate of lime trace. 



Sulphur trace. 



Silica 8.59 



Sesquioxides of iron and alumina 3.51 



100-05 



From this it will be seen to have much less silica and alumina than 

 the beds on the Milwaukee river. 



