MOUNT GREYLOCK. 189 



tinii generally occurs in the Grreylock mass the actual thickness is probably 

 less than the minimum figures given in the table, and may possibly be 

 considerably less. It will be observed, however, that the maximum thick- 

 ness of the entire series does not exceed the minimum thickness attributed 

 to the Lower Silurian rocks in the Appalachian region. 1 



GEOLOGIC AGE. 



The question of the age of the beds of < ireylock, and the treatment of 

 the whole subject from the standpoint of historic geology are beyond the 

 province of this report, but the various conclusions which have been reached 

 and are being reached in regard to the geologic age of these formations are 

 added in separate columns for convenience of reference. 



Se« J. D. Dana, Manual of Geology, third edition, pp. 192, 210. 



