HELDERBERG GROUP. 27 



porous character. The better quarry-stone furnishes sills, door- 

 steps, etc., but most of it is used for the production of lime. Its 

 composition is : 



Carbonate of lime 84.0 



" " magnesia 13.0 



Iron oxide hydr. ._ 0.4 



Quartz and bitumen 2.2 



99.6 



The deeper strata of the quarry become worthless from a 

 copious admixture of white, cherty concretions. The exudation of 

 rock oil from the crevices induced some persons, a number of years 

 ago, to form a company to bore for rock oil at this locality. A 

 drill hole was sunk to the depth of 700 feet, but without the 

 hoped-for success. The record of the boring I could not obtain. 

 I was informed that not many feet below the rock beds opened 

 in the quarry, a bed of sand rock was struck. This sand-rock de- 

 posit seems to be a very constant stratum found at that horizon, 

 not only in Michigan, but all over the Helderberg area of the State 

 of Ohio. Natural outcrops of this sand rock can be observed in 

 the bed of Raisin River, six miles above Monroe ; it is there very 

 hard and compact, rich in calcareous cement ; several fossils, 

 casts of spirifer, etc., are inclosed in some blocks of the rock, but 

 they are too imperfect for specific determination. The sand-rock 

 stratum, in a soft, friable condition, and occasionally perfectly white, 

 is found in the northeast corner of Raisinville township, on the 

 farm of Mr. Bond, where it forms the surface rock over a good 

 many acres of ground ; in places it is overlaid by dolomitic lime- 

 stones about 8 feet in thickness, which contain the casts of 

 numerous fossils, Zaphrentis, Favosites, several forms of Bryozoa, 

 Atrypa reticularis, Orthis Livia, Conocardium trigonale, Phacops 

 bufo, Dalmania selenurus. Quantities of this sand, which is almost 

 pure quartz without admixture, have been shipped to Pittsburgh for 

 glass manufacture, for which purpose it is said to be of excellent 

 quality. The thickness of the deposit is not seen in this place ; 

 only 6 or 7 feet are denuded in the diggings. In Section 16 

 of Ida township, a sand rock of about 6 feet in thickness forms 

 the top layers of a limestone quarry. The upper strata are friable 



