304 Dr. John T. Plummer on the , 



It has appeared to me that these travelled specimens have at- 

 tracted too little notice ; a minute inquiry into their composition, 

 instituted all over the country, would probably be repaid by sev- 

 eral interesting developments of a nature the geologist can easily 

 foresee. Even a careful collection of the reports already made 

 on this subject would be useful. 



The largest bowlder I have found in my limited district, would 

 weigh by calculation about forty three tons. In general these 

 rocks are much smaller, and altogether they are not very numer- 

 ous. In some situations, hundreds of them of movable size are 

 thrown together, while usually, they are not sufficiently large 

 and common to excite attention. As an approximation to the 

 number of bowlders may be of some service, in comparing this 

 district with others, I will state that after a careful survey of an 

 area of one hundred and forty four miles, forming a square around 

 Richmond, I suppose that if the bowlders two feet and upwards 

 in diameter were equally distributed over this surface, they would 

 not vary much from three hundred and twenty to each square 

 mile ; which would give to the whole area specified, forty six 

 thousand and eighty bowlders of the dimensions above stated. 



The large bowlder mentioned, rests, with many smaller ones 

 and another nearly its equal, in a peat-field in the northern sub- 

 urbs of Richmond. All of them are granitic rocks, and they 

 probably repose upon the wet gravel and clay which lie beneath 

 the peat ; the peat is about three feet deep. 



I proceed to enumerate very briefly the chief varieties which 

 have found their way into this section of country, embracing all 

 kinds of transported fragments, regardless of their bulk. I have 

 collected and labelled upwards of seventy easily distinguishable 

 specimens, but in the present enumeration I shall be more gene- 

 ral. Perhaps the most convenient division for my purpose, will 

 be into siliceous and non-calcareous, and calcareous kinds, and I 

 will therefore arrange the specimens under these two heads. 



Siliceous and N on- Calcareous. 



1. Almost every variety of granite, gneiss, sienite, and of green- 

 stone. These constitute the larger masses, and the greater pro- 

 portion of the drift ; and they sometimes contain garnets, mag- 

 netic oxide of iron, and other minerals. Mica slate is seldom 

 found. 



