THE NATURAL HISTORY SURVEY. 37 



carbonate, filtered and precipitated magnesium with sodium 

 phosphate. The amount of magnesium was found to vary in 

 different specimens. A very large percent being found in 

 dark colored small crystals lining cavities in the limestone 

 found on the lake shore. Smaller percents were found in 

 crystals coating a cellular limestone from the drainage canal, 

 and none was present in calcite crystals imbedded in the 

 asphalt which was collected at Stony Island. 



Siderite. FeCO 3 . Hexagoual. 



Siderite occurs as incrustations on the Niagara limestone. 

 All the specimens observed are too imperfect to illustrate the 

 crystal habit or the physical characteristics of the mineral with 

 any degree of perfection. Noticeably in the calcium and 

 magnesium carbonates does the presence of the iron carbonate 

 increase the specific gravity, which, for dolomite is 2.8 to 2.9, 

 while for siderite it is 3.8. The hardness of siderite is 3.5 to 

 4.0. Its color is usually grey, brown, or brownish-red. It 

 becomes magnetic upon ignition, and effervesces in acid. 



Aragonite. CaCO 3 Orthorhombic. 



The specimens which seem to belong to this species thus 

 lar found are too small to permit of adequate determination. 

 Some of the stalactites which by their radiated structure sug- 

 gest one of the common occurrences of aragonite gave by the 

 above described method for the detection of magnesium results 

 which would place the stalactites with dolomite, but none of 

 the literature on the subject describes dolomite as occurring in 

 stalactites. Further examination, however, would be necessary 

 to determine whether these stalactites disclose biaxial proper- 

 ties such as are necessary for aragonite. Here and th'ere on 

 the stalactites are microscopic crystals of an iron sulphide, and 

 these increase the amount of iron in the analyses. Aragonite 

 resembles calcite in physical properties and occurrence. 



Malachite. CuCCV Cu(OH) 2 . Monoclinic. 



The only occurrence of this mineral in the region under 

 consideration is illustrative of its genesis and relation to other 

 forms of copper. It appears as a light green coating on the 

 native copper specimens found in the drift. This is another 

 illustration of the metamorphism which produces copper car- 

 bonate on the exposed parts of veins composed of chalcopy- 



