of Shropshire and parts adjacent , 81 
cause of the numerous rapids and rocky ledges, and deep pools by 
which this river is so remarkably distinguished. 
The most rapid part of the course of the Dee is between Corwen 
and Llangollen, where it falls over ledges of rock, and its channel is 
Contracted by the near approach of the steep banks. The perpendi- 
cular fall through the latter six miles of this space, namely from 
Llandysilio to Pontycysyllte, as estimated from the feeder of the 
Ellesmere canal, is at least 131 feet, being at the rate of 22 feet per 
mile, which is by far the steepest descent that I have as yet had an 
opportunity of measuring. The remainder of its course to tideway 
at Chester, is about thirty-four miles, during which it falls 174 feet, 
being at the rate of 5 feet 1 inch per mile. In its natural state it is 
wholly innavigable, but by means of a weir at Chester, the water i§ 
held up so as to allow the passage of small boats for two or three miles. 
I shall mention only one more river within this district, namely 
the Stour. It rises about two or three miles north of Wolverhampton, 
and after a course of twenty-seven or twenty-eight miles falls into 
the Severn at Stourport. The entire country through which it 
flows is coarse sand, sandy gravel, or friable red sandstone. Its 
source is at least 130 feet lower than the basin of the old canal at 
Birmingham, and therefore it may be considered as belonging rather 
to a flat country ; its entire fall however is 294 feet, being at the 
rate of 10§ feet per mile. 
If the above facts and the deductions which obviously flow from 
them are of importance even when relating to a district of compara- 
tively small extent ; if they tend, as I think they do very materially, 
to elucidate the physical geography of a country, and by consequence 
a very interesting part of geological research, namely, the present 
diversity in the surface of the earth, and the cause of that diversity, 
it is manifest that the more these observations are extended, the 
VOL. V. L 
