20 
the interstices being filled with smaller pebbles and coarse 
. sand. I also found a pebble of sandstone, the grains of 
which are of a peculiarly translucent quartz. These were 
from the ridge behind High Bradley. 
Next we have another great series of fine-grained sand- 
stones and shales, forming the body of the hills surrounding 
Xeighley under their outlying caps of Eough Rock. In this 
vast thickness of strata, any bed which can be identified, 
wherever it occurs, by its physical characters, is like a land- 
mark to the home-bound sailor — it tells us where we are in 
the series, no matter how many cross- gales in the shape of 
faults we may have encountered in traversing a district. 
Such a bed we have for instance in the grit forming the 
fine escarpment of Otley Chevin, and extending with sundry 
shiftings of small faults, to the Aire at Hawk Clifi*, whence 
it continues westward, overhanging the Glusburn Valley. 
Without such a landmark, it is evident that after crossing a 
line of fault, we should at once be out of our reckoning, 
though, unlike the mariner, we can always put back into 
port and start again by another route, so as to avoid faults. 
The Rough Rock is the highest group of the Millstone 
Grit series. Its upper part is always a coarse grit or con- 
glomerate, whilst the lower part, as at Haworth and Culling- 
worth, is fine grained and flaggy. The Cross Roads 
quarries are good sections of the lower part. Sometimes 
the entire mass is coarse conglomerate, as the Druid's 
Altar escarpment between Keighley and Bingley., From one 
of the blocks near the Altar I got a slightly roUed 
pebble of felspar, not in the least degree decomposed, 
though protruding from a weathered surface. I also 
found felspar pebbles in the deep gully behind Harden, 
and in Hog Holes Delf. Some of them were so little worn 
as to show that the crystals of which they were formed were 
the usual square and rhomboidal prisms. In Hog Holes 
