THE ORIGIN OF THE INCLUSIONS IN DIKES 



i8i 



less than that of the magma. In the other cases where the inclu- 

 sions have sunk, the fragments are composed of various rocks 

 including quartzite, sandstone, slate, limestone, gneiss, and diabase. 





Movement of Inclusions 



Examples 



None 



Up 



Down 



Cornwall 



X 

 X 

 X 

 X 







Mexico. 







Cape Ann 







Montreal 



3,000 ft. 



2 000-(-ft. 



Marblehead . 



I ooo-|-ft. 



Southern Sweden 







X 



Cripple Creek . 







X 



Pequawket 







X 



Brazil 





I2,000 + ft 



X 

 X 

 X 

 X 

 X 

 X 

 4,000 ft. 



X 

 24,000 ft. 



X 



Shelburne Point 



X 





jNIancos 





Aschaflfenburg 







Somerville 







Rossland 







Ogunquit 







Little Belt Mountains 







Syracuse 



X 

 X 

 X 





Beemersville 





Crazy Mountains 









• Inclusions in dikes are in general rounded when they have 

 come from some depth and angular when near the place of origin. 

 This indicates that the rounding is largely due to friction which 

 varies with: (i) the distance through which the inclusion has 

 moved, (2) the number of the inclusions; (3) the width of the dike, 



(4) the temperature of the inclusion at the time of the shattering, 



(5) the rate of movement of the inclusion. 



The initial temperature of the outside of an inclusion is the mean 

 between that of the magma and that of the center of the inclusion. 

 Hence, if there is a fused contact around an inclusion or if the latter 

 shows resorption, a high temperature of the whole fragment is 

 indicated. As most dikes are quickly chilled, it is seldom possible 

 to heat cold inclusions to a temperature at which fusion can 

 take place around their peripheries. In dikes several hundred 

 feet wide, as those of southern Sweden, cold inclusions may be 

 heated to such a high temperature that partial resorption results. 

 In narrower dikes, partial resorption of fragments is possible only 



