310 Dr Smith on the Composition of the 



quartzose mica slate. Though very insoluble in their nature, 

 these rocks will, by slow decomposition, yield to the water 

 minute portions of silica, potash, and iron. The springs of 

 the Dee must, however, be very pure. Further down, the 

 river receives water that flows over patches of crystalline 

 limestone, and a tributary (the Muick) passes along a ser- 

 pentine range. From these rocks, the water will derive a 

 small proportion of lime and magnesia. Proceeding still far- 

 ther down, the rocks present no variety : granite and gneiss, 

 with occasional veins of felspar-porphyry, and more rarely, 

 patches of limestone, making up the geology of the district. 



The water for the supply of Aberdeen is taken from the 

 Dee about two miles from its mouth, and quite beyond the 

 reach of the tide water. It percolates through the gravelly 

 sides and bottom into drains, and is thence pumped up to the 

 highest level of the town. It is distributed through iron 

 mains, and taken into houses by small lead pipes, to which 

 lead cisterns, generally of moderate dimensions, are com- 

 monly attached. The supply is constant, and amounts to 

 about one million gallons per day. 



The district drained by the Don, lies immediately north of 

 that drained by the Dee, and is of much less extent. Rising 

 in mossy ground, encircled by granite hills, on the borders of 

 Banffshire, the Don pursues a winding course of about 60 

 miles to Aberdeen. A straight line from its origin to its 

 termination is about 42 miles. The mountainous region 

 drained by the sources of this river, although mainly granitic, 

 has more limestone and serpentine than exist about the Dee, 

 and hence more lime and magnesia might be expected in the 

 water. At Kildrummy, the Don passes through a range of 

 old red sandstone. A few miles below this the hills recede 

 from the river, and enclose the fine valley of Alford. After 

 emerging from the hilly country at Monymusk, its progress 

 is tortuous and slow, through alluvial meadows and an open 

 country, till within a few miles of its termination, when it 

 again flows rapidly. About 18 miles from the sea it receives 

 its largest tributary, the Ury, which drains a fertile country, 

 and has a course of about 24 miles before losing itself in the 

 Don. After rain, the water of the Ury is commonly tinged 



