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tlie deptli of one foot, giving great prominence to these forms. But 

 owing to their frangibility and easy cleavage, they could rarely be 

 removed intact. 



We may certainly infer from this that the phosphate mineral is less 

 acted upon than the surrounding limestone, and yet, if these crystals 

 are entirely liberated and exposed to a moist atmosphere they soon 

 undergo disintegration. 



The rounding of the angles of these crystals has drawn forth many 

 theories respecting their disfigurement, fusion being offered as an 

 explanation by some mineralogists, whilst others attribute it to a sol- 

 vent action. Now, whether we adopt the igneous theory, or that of par- 

 tial solution, serious objections may aiise to refute either. In the first 

 instance, qiinerals easily fusible and yet preserving their sharpness of out- 

 line, are found associated with rounded crystals of a less fusible apatite. 

 Than again, we meet with rounded crystals of pyroxene (although much 

 more rare) imbedded in limestone, also enclosing rounded crystals of 

 apatite. Now, it is hard to understand how the apatite and pyroxene 

 alike should be attacked by the action of a solvent, when the latter 

 mineral is almost insoluble. Some aluminous varieties ai-e, however, 

 decomposed with great diificulty by sulphuric acid at the temperature 

 of 250"^ c. It frequently happens that crystals of apatite assuming 

 sharp angles are indiscriminately mixed with others that have been 

 rounded, imbedded in the same limestone. On the other hand i# rarely 

 happens that crystals lining the walls of fissures have their angles 

 rounded, although frequently one or more of their faces are obliterated 

 or otherwise contorted, probably due to an interrupted crystalizution. 

 Bent or broken crystals that have been receniented are of common oc- 

 currence. The same crystals often enclose calcice, and others again 

 have cavaties extending the whole length of the crystal, are entirely 

 empty, or contain a rounded pebble of cleavable calcite. 



I should like to engage your attention foi' a few moments on the 

 occurrence of this mineral in Hull and Wakefield. At an opening 

 known as the " Gow Mine," in Hull, a pit has been sunk 150 feet in 

 limestone, parallel to the wall of a large fissure which may be said to 

 characterize this band for several miles, it being made the more con- 

 spicuous by the abundance of crystals everywhere adorning its walls. 



