ASSOCIATED METAHORPHTC ROCKS OF THE LAKE-DISTRICT. 



575 



cavities generally occur in plenty ; but these seldom exceed ^uW 

 of an inch in length, and in them^the bubbles either have no move- 

 ment or but a very slight or sluggish one. 



In Plate XXX. I have figured examples of liquid-cavities from dif- 

 ferent quartz-bearing rocks of the district, and appended a scale of 

 Yjjoj) °f an inch magnified to the same amount as the drawings, 

 and divided into 20,000ths. It will be seen that in most cases the 

 general form of the cavities is rectangular, or more or less irregular ; 

 but in some instances, as particularly in figs. 44, 46, 47, 50, and 62 f 

 it partakes of the true crystalline form of the quartz, showing a six- 

 sided section, and representing a kind of negative crystallization. 



III. General Results of Examination. 



Preliminary Remarks. — After having made above 500 drawings 

 and measurements, I find the following to be the general results for 

 the various quartz-bearing rocks enumerated below: — 



The figures given under v represent the means of many measure- 

 ments taken from different slices of the same rocks at various spots. 

 I cannot but feel, however, that the number of observations is com- 

 paratively small, and should therefore like to consider the results 

 obtained as merely preliminary to a more extended investigation, 

 which might be undertaken at some future time under circumstances 

 of greater leisure. 



It will be understood that the figures given below represent the 

 relation existing between the size of the liquid-cavity, as a whole, 

 and that of the vacuity ; thus, if the latter be one sixth of the former, 

 the relationship is represented by '166. 





v. 



Pressure, 

 p. 



Skiddaw Granite 



•130 

 •166 

 •166 



•125 

 •150 



•190 

 •170 

 •140 



•150 



52000 

 42000 

 42000 



53000 

 46000 



35000 

 40000 

 49000 



46000 



Eskdale Granite 



„ „ , veins from 



Quartz Eelsite (Elvanite) dykes from the Esk- 

 dale Granite 



Shap Granite 



Ennerdale and Buttermere Syenite (or Syenitic 



Granite) 



Quartz Eelsite of St. John's Yale 



Quartz Eelsite of Fairy Crag, Crag Bridge .... 

 Quartz Eelsite (Elvanite) dyke of Armboth and 



Helvellyn 



Mean of all the above 



•158 



44000 





Making use of the formula given in Mr. Sorby's paper, 



^=369,000^, 

 Q. J. G. S. No. 124. 2 a 



