194 
SUB -AERIAL DENUDATION 
Shales, and a little gully marking the point where the Lower 
Limestone Shales cross the Avon, there are five tributary 
streams on the Somersetshire side of the Avon. 
The first, which I have marked on the map as the Leigh 
Brook, collects the rainfall in a Lower Limestone Shales 
depression N.E. of Abbot’s Leigh, and in a depression of the 
Limestone on the Leigh Court estate. The two depressions 
join near the keeper’s lodge, whence the little stream flows in a 
prettily wooded notch of the Old Red Sandstone until it reaches 
the Avon. 
The second, which I have marked as the Oakham Brook, 
answers to the Stoke Trym on the Gloucester side of the river ; 
but with this difference, that it folio w's the depression to the 
Avon and does not cut a gorge in the Dolomitic Conglomerate, 
which steeply bounds it on the W., resting on the upturned 
edges of the Old Red. 
The third, or Chapel Brook, collects the rainfall from the 
Lower Limestone Shales depression S. of Abbot's Leigh, in the 
manner shown in the map. It then leaves this depression, and 
notches the Old Red Sandstone ridge, near the N. side of which 
it is dammed back to form the Abbot’s Pool. After this its 
valley opens out, right and left, as it crosses the softer Old Red 
rocks, and it receives a little tributary from the W., the 
depression being less marked on the E. owing to the overlie of 
Dolomitic Conglomerate. After crossing this depression, the 
valley of the Chapel Brook narrows to a wooded cleft as it passes 
through the harder Dolomitic Conglomerate ; opens out again 
where the softer Triassic Marls come in ; and narrows once more 
in the harder Dolomitic Conglomerate through which it finally 
passes to the Avon. 
The fourth, or Markham Brook, follows a very similar course. 
It collects its head-waters from the Leigh Downs, and from the 
E. and VV. depression of the Lower Limestone Shales. It, too. 
