Yorkshire Naturalists at Hebden Bridge. 295 
sandstone are strewn along the sides of the valley, while others 
have rolled down. into the river bed. 
From the foot of the Dene to Lumb Falls, the Yoredales 
or Pendlesides were found to be exposed along the stream 
sides with the exception of a short distance where the Wet 
Ing fault, with a downthrow of about 35 yards, bring the 
Kinder grits into the bottom. 
The hard nodular bands of limestone which occur on the 
left hand side of the stream just above the fault were worked 
for a little while, and a few fossils, Aviculapectens and Gontatites 
were obtained. 
At Lumb Falls the formation of water-falls was well illus- 
trated. The shales are overlaid by the hard band of Kinder 
grits over which the stream flows, and as the continued swirling 
of the water wears out the softer material, the harder step 
which forms the fall is constantly breaking off and gradually 
receding. Several flat places on the hillsides were pointed out 
as old river terraces. 
Mr. Abraham Newell records the presence of a number of 
pot-holes in Nutclough, both in the bed of the stream, and on 
inclined and vertical sides of the rocks. The generally accepted 
theory imputes them to the grinding action of sand and pebbles 
set in swirling motion by wind or water. Personally, I con- 
sider that the alleged motion seldom takes place, and if it does 
the grinding effect is very feeble. Obviously this action cannot 
take place on upright faces of rocks. The potholes noticed 
during the excursion are coincident in horizon with beds in 
which nodular concretions are abundant wherever quarries 
are opened. These statements hold good throughout the Kinder 
grit and Haslingden Flag districts, where are thousands of pot- 
holes, whether in a clough or the open country. The nodules, 
being composed of more easily eroded material than the surround- 
ing rock, have been disintegrated and removed, leaving cavities 
behind. Thus every pothole represents a once existing nodule, 
LEPIDOPTERA.—Mr. E. B. Gibson writes :—Lepidoptera 
were very scarce, and none but common species were obtained. 
Tortrix viridana was abundant and in fine condition. Metro- 
campa margaritaria, Cidaria populata, Tortrix ministrana and 
T. fosterana were the only other species observed. 
HyMENOPTERA.—Mr. Rosse Butterfield reports :—Dr. A. 
Wilman and I explored Crimsworth Dene for Hymenoptera 
and Diptera. Commencing at Lumb Bridge we worked down 
the valley to the bottom. The lower part of the Dene seems 
favourable for the Fossorial Hymenoptera, but on the day of 
the Union’s excursion the sun did not gain sufficient power to 
induce these active creatures to fly. On both sides of the 
valley several large nests of the ant, Formica rufa, were found, 
and a careful though fruitless search was made for Formi- 
1915 Sept. 1. 
