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correctly on the edge of the small Nailsea Coal basin, which forms the 
S.W. portion of that larger Coal field. From time to time during our 
excursions I have attempted to lay before our members the main features 
of this Coal field extending in a triangular form from Cromhall as its 
apex, to the range of the Mendip Hills as its base (whose probable total 
area is 240 square miles, whose exposed area is 48 square miles), and I 
venture to say if you have been able to master the varied formations 
contained within this district, you have made yourselves masters of some 
of the most knotty points in Geology, and will be able to form a 
very fair notion of the whole coal area of England. We will, how- 
ever, to-day confine our remarks to some of the features of the Nailsea 
basin. The origin of these basins I have before attempted to describe. 
Well, this Mountain or Carboniferous limestone forming the sides of 
the basin and resting conformably on the Old Red sandstone, may be 
traced nearly the whole way from Tortworth on the N., to Almonsbury, 
Westbury-on-Trym and Durdham Down. Here the Avon gorge cuts 
through it and forms the division between Durdham and Leigh downs. 
From the latter down it extends westwards by Cadbury camp to Clevedon, 
where it meets another ridge of the same formation which runs along the 
coast from Portishead by Walton down ; at this point of meeting they 
probably form one continuous ridge, which runs on beneath the Channel by 
Woodspring point to the Steep and Flat Holmes, whilst Backwell and 
Broadfield ridge continues beneath the alluvial plain to Worle hill. The 
Mendip range likewise running on beneath the Channel from Brean down 
to the Steep Holmes. The general dip being N. and §., the principal mass 
of Limestone (or its strike) therefore runs E. and W. From this brief 
general description you will see that the shape of the district is that of a 
trough or basin, bounded on all sides by the Carboniferous limestone. 
The range of downs we are now standing on forming one side, Broadfield 
down the other, the Mendips and Brean down the third. I said that the 
Carboniferous limestone rests conformably upon the Old Red sandstone, 
and this is the case ina general way throughout the district, save where 
here and there a fault brings some other formation in juxtaposition, as we 
see near ‘Naish House,’ about a mile to the E. of Cadbury camp. Here 
the Coal measures themselves are brought down against the Carboniferous 
limestone by a downthrow of the Old Red sandstone. During our morning’s 
walk we passed, if you remember, over the Pennant sandstones, a part of 
the Coal Measures, in a quarry on the slope N. of the Down. The 
Coal Measures take the proper position of the Old Red from this 
point to Clevedon, a distance of five miles. This fault runs parallel with 
ee 
