THE 



QUARTERLY JOURNAL, 



.April, 1821. 



Art. I. On the Forms of Mineralogical Hammers. By 

 J. Mac Culloch, M.D., F.ll.S. 



[Communicated by the author.] 



X HOSE who have not been very conversant in countries con- 

 sisting of primary and trap rocks, will not easily believe how 

 difficult it is to procure specimens from many of these substances 

 by means of any of the hammers in common use. This is 

 more particularly the case with some of the members of the 

 trap family, which are often characterized by an uncommon de- 

 gree of toughness or tenacity ; and it is not uncommon in 

 those granites which are of a fine grain, and which contain a 

 conspicuous proportion of hornblende. In those varieties of 

 gneiss in which compact feldspar predominates, in some of the 

 members of the primary sandstone series, and in the varieties of 

 hornblende schist in which the laminar structure is obscure or 

 wanting, the same difficulty frequently occurs, and to such a 

 degree as absolutely to defy the utmost efforts of the heaviest 

 hammers in common use, whether by stone-masons or mineralo- 

 gists. Serpentine also very often, and diallage rock almost 

 always, present such a resistance as to deprive the collector of 

 the power of obtaining satisfactory or sufficient specimens ; but 

 it is unnecessary to enumerate all the rocks which those who 

 arc in the least conversant with this department of mineralogy 

 must occasionally have abandoned in despair. 



Independently, however, of the wish to obtain a mere speci- 

 men, such as can first be detached, it is often desirable to ob- 

 tain a deep access to the rock under examination, on account of 

 the changes which the superficial parts undergo froin the loss of 



Vol. XI. B 



