114 DOLOMITE. 
extreme slowness, whilst it will readily dissolve calcite at 
the same temperature even when more dilute. The same 
authority also states that whilst water containing carbonic 
acid will dissolve calcite, Dolomite is not attacked by it. 
Dolomite is found in the massive form in all states of 
aggregation; in easily cleavable masses, sometimes very 
fine grained almost earthy in fracture, and, in most English 
"localities, highly crystalline and saccharoidal. It is found 
principally in England in beds of the Permian period, but 
it also occurs in all geological ages from the Silurian period 
upwards. The following is an average of several analyses 
made by myself, of specimens of the yellow highly crys- 
talline Dolomite which occurs abundantly in the Permian 
formation of Nottinghamshire and E. Derbyshire: 
Insoluble Siliceous Matter - 1°88 
Alumina and Peroxide of Iron 2°58 
Lime - - - - - 30°45 
Magnesia - - - - - 20°07 
Carbonic Acid - - - 45°01 
99°99 
Here it will be seen that the magnesia and lime are to 
one another in the atomic relation of 100: 108, hence this 
rock is a true Dolomite. In the Permian formation, mag- 
nesian limestones are found containing from five to twenty 
per cent. of magnesia which are not Dolomites, and for 
this class of rocks I propose to use the generic name of 
magnesian limestone. We may accordingly expect to meet 
with the following series of rocks. 
tst. Limestone containing magnesite, usually in less 
proportion than is required to form Dolomite; there are, 
however, a few instances on record where the proportion of 
magnesia exceeds this amount; such rocks may be looked 
upon as magnesite containing calcite, 
i ae 
