48 



fragments of CWnnefo. some beds full of these remains. Other strata contain 

 masses of corals in fine preservation, belonging to the group of reef-building 

 genera. The teeth and fin spines of large shark-like fishes are likewise found in 

 these rooks. Those who desire to see the grandest section of all the beds of the 

 Carboniferous Limestone in our country I should recommend to visit the gorge 

 of the Avon, near Clifton, where they will find this rock in its relative position 

 to the Old Red Sandstone below, and the Millstone grit above. The entire 

 thickness of the rocks here exposed is about 4,056 feet ; of these the Millstone 

 grit is 1)50 feet, the Carboniferous Limestone 2,338 feet, and the Old Red 

 Sandstone 7(33 feet. Nearly every bed may be examined and measured in situ 

 and the changing conditions of the old sea bottom ascertained by a careful study 

 of the successive beds as they lie inclined upon each other in this most in- 

 structive and wonderful section. Understand then that the Carboniferous 

 Limestone was a great marine form ition, for on it lies the Coal Measures which 

 are for the most part lacustrine or fresh water deposits. 



Before passing from the Carboniferous Limestone, permit me to point out 

 to you the physiographical features of the landscape in a region where Mountain 

 Limestone forms the prevailing rock. You see the fine old mural escarpment 

 of the Cold well rocks, and as you descend the Wye you will find other bluffs of 

 a like character, although in none do you discover such a beautiful picturesque 

 effect as in that rich peep below you. In the Mendip hills, and in Derbyshire 

 peaks and Tors, and in the Mountain Limestone districts of Yorkshire and 

 Northumberland, you will find the same physical features as in the scene now 

 lying before you on the banks of the Wye. Every rock formation has its own 

 physiographical features, its special outline, its internal structure, and the 

 forms of life embedded in it, have likewise their own individuality, 



The carboniferous rocks of the Forest of Dean form the gentle swelling 

 outline of hills lying to the eastward of our present position. They consist of 

 Coal Measures with 32 beds of coal 2,400 feet, Millstone grit "or Farewell rock 

 455 feet, Carboniferous Limestone 480 feet, and Lower Limestone and Shale 165 

 feet. So that the total depth of the Coal Measures of Dean Forest is about 

 2,765 feet, according to the accurate measurements of Mr. D. Williams, in the 

 Memoirs of the Geological Survey. Bly friend, the Rev. P. B. Brodie has 

 already given you a lecture from this place on the Natural History of Coal, 

 and I must refer you to the Volume of your Transactions for 1866, for an account 

 thereof. 



Between the Dean Forest and the Cotteswold Hills we traverse a portion 

 of the valley of the Severn. Here are developed the New Red Sandstone, Red 

 Marls of the Keuper formation, and super-imposed on them, the Bone-bed, and 

 lower Lias Lime-stones and Shales, and here commences the Second Volume of 

 the great rock book, all the forms of animal and vegetable life that abounded 

 in the seas and land of the Palaeozoic period had passed away, and no single 

 species that lived in that first period of the world's life is found in that upon 

 which we now enter. Great elevations of the earth's crust took place at the 



