AND THE AVON GORGE. 
195 
then notches the harder Old Red, flowing in a narrow valley, 
which widens out in the softer Old Red, and here receives a 
tributary from near Failands House, and a smaller intermittent 
streamlet from the E. Its valley, too, then narrows to a wooded 
cleft, as it passes through the harder Dolomitic Conglomerate, 
giving rise to Markham Bottom ; opens out in the Triassic 
Marls above Pill ; and then narrows again in the Dolomitic 
Conglomerate, just before it falls into the Avon. 
Nothing could be more beautiful than the way in which 
these two streams, the Chapel Brook and the Markham Brook, 
exemplify the differential action of general and special denudation. 
Where the rocks are hard the valleys are narrow, for here 
general denudation cannot keep pace with special. Where the 
rocks are soft the valleys open out, for here general denudation 
has greater power. At the present relative level of sea and land, 
the special denudation is going on very slowly, or has almost 
ceased. But were the land to be elevated to a greater height 
above the sea level, the more rapid streams would cut their way 
downwards far more rapidly into the rocks over which they run. 
In times past, no doubt, at periods of greater rainfall, the streams 
were more active agents of denudation than they could be with 
their present dimensions. A more rapid fall, and a larger water 
supply, probably marked the period of the greatest activity of 
these streams. 
The fifth and last stream, the Easton Brook, rises in the 
softer Old Red beds and then notches the Dolomitic Con- 
glomerate, at first so deeply as to expose the underlying 
Old Red Sandstone. After emerging from the constricting 
Dolomitic Conglomerate, it passes through Trias Marls, and 
finally over the Severn flats to join the Avon a little S. of 
Avonmouth. 
The lover of nature will find the tracing of such streams as 
these, downwards from their source, a most delightful occupation. 
p 
