70 



FEANK D. ADAMS OX THE 



thin, and the clay and the sand being of the same colour, it was not possible to dis- 

 tinguish them until the upper bed of clay slid off the lower. 



" Boulders were occasionally struck, some of them containing two or three cubic 

 yards. 



" The large boulders were not numerous ; perhaps there were not more than half 

 a dozen of them. I am now speaking of boulders too large to pass through the com- 

 partments of the shields ; of small bonlders there were a considerable number. They 

 were all, so far as I know, coarse granite. The workmen used to call them 'bastard 

 granite.' 



"The bed of the river consists of sand and gravel, varying in thickness Irom a few 

 inches to several feet." 



In order to ascertain the proportion of sand and gravel present, weighed portions of 

 the several samples were submitted to a process of washing or elutriation, being repeat- 

 edly stirred with successive portions of water and allowed each time to settle for ten 

 seconds ; in this way only the clay and the exceedingly fine sand were removed. The 

 gravel and the rest of the sand remaining behind were then weighed. The amount of 

 carbonic dioxide present in the several samples was also kindly determined by Mr. A. 

 Klock, under Dr. Harrington's supervision, in the chemical laboratory of this University. 

 These results, together with the amount of carbonate of lime represented by the carbonic 

 acid in each case, are given in the following table : — 



It may here be mentioned, however, that a certain amount of magnesia is probably 

 present in combination with lime and carbonic aeid, forming adolomitic limestone rather 

 than a pure carbonate of lime. 



Nos. 1 and 2 when boiled with concentrated hydrochloric acid for au hour left 683 

 per cent, and 688 per cent, of insoluble residue respectively. 



The following figures showing the amount of calcium carbonate in brick clays from 



