278 DESCRIPTION OF THE MUSEUM. 



case on our right, we shall follow their nume- 

 rical order. 



The first series is that of calcareous substances, 

 or those which contain lime in a greater or less 

 quantity. The carbonate of lime begins the 

 range : the numerous modifications of this sub- 

 stance, the most abundant on the globe, almost 

 entirely occupy the five first cases. We may first 

 observe on the stage a suite of crystallized varie- 

 ties for study, each of which has a characteristic 

 name. Some places, although vacant, are labelled 

 to mark those known varieties which are still 

 wanting to complete the series. Below the 

 stage, in the first case, is a very fine crystal of 

 Icelandic calcareous spar, which exhibits to pecu- 

 liar advantage the property of double refraction, 

 for which this mineral is remarkable. This spe- 

 cimen, of an uncommon size and clearness, is 

 nearly seven inches thick. We also see some very 

 interesting groups of crystals on the shelves ; 

 amongst them the primitive carbonate of lime 

 from Ratieborztiz, in Bohemia ; also metastatic 

 crystals from Derbyshire, given by M. Heuland, 

 a German mineralogist, to whom the Museum is 

 indebted for a great number of specimens, all 

 remarkable for their size and freshness. Here 

 too we see the equiaxe variety from Andreasberg, 

 in Harz. The two following cases present a 



