T06 LOWER PENINSULA. 



by experience that the depressions indicate places where the super- 

 ficial gypsum beds have been dissolved, or carried away by some 

 cause, while in the hillocks he is always sure to find a well-pre- 

 served mass. In the quarries of Messrs. Smith, Bullard & Co., the 

 superficial gypsum bed is 15 feet thick; large masses of white or 

 rose-colored granular gypsum and smaller fragments of the same 

 pure substance are cemented together by seams and veins of gray 

 argillaceous gypsum into one solid, compact bed, variegated and 

 mottled in some spots like castile soap, or of much coarser brecciated 

 structure Avhere the larger masses of pure gypsum are cemented. 

 Below the gypsum bed follow calcareo-arenaceous, thinly lami- 

 nated flagstones, and shale beds of dark greenish drab-color, seen 

 uncovered in a thickness of about 6 feet. The flagstones are very 

 fossiliferous ; particularly abundant is a Myalina, next so are Al- 

 lorisma, Aviculopecten, Edmondia, Retzia globosa, and Spiriferina 

 spinosa. The owners of the quarry have bored to the depth of 20 

 feet below its bottom, and have found only a few feet down another 

 very thick gypsum bed, which for the present is not opened. 

 About 4 miles south of Alabaster Point, the gypsum formations rise 

 in bluffs along the shore to the height of about 25 feet. The strata 

 in question seem to be next above the gypsum of the Alabaster 

 Point quarries. Lowest, at the water level, heavy, somewhat con- 

 cretionary masses of gypsum project; above them follow about 10 

 feet of soft green shales full of small nodular concretions of gyp- 

 sum. The shales are covered by an arenaceo-calcareous rock, in beds 

 of from 4 to 6 inches in thickness, which in one place where gyp- 

 sum has been quarried is directly covered by drift masses, the sur- 

 face of the ledges being plainly drift-marked in a direction from 

 northeast to southwest. Only a few steps further south from this 

 locality, these upper drift-marked ledges are overlaid by from 6 to 

 8 feet of arenaceous shales, or by soft greenish sandstones of dis- 

 cordant stratification, and frequently ripple-marked ; and on them 

 a seam of brittle limestone 15 inches or 2 feet thick, with many 

 flint concretions, forms the top of the bluffs. This calcareous 

 rock with flint nodules forms the surface rock under the drift, ex- 

 tending from here down to White Rock Point, where a number of 

 additional light-colored limestone beds are found connected with 

 it, and laid open in a few limited escarpments along the lake 

 shore. Next above these limestones of White Rock Point follow 



