ON A PIECE OF LIMESTONE. 16; 



O^ A PIECE OF LIMESTONE.' 



By WILLIAM B. CAKPENTEK, LL.D., F.E.S. 



IN selecting a subject lor the lecture which, at the request of the 

 council of the British Association, I undertook to give you during 

 its present meeting, I have been guided by the desire to tell you 

 something that would be new to you in regard to matters with which 

 you are already familiar, and to connect this with the results of my 

 own deep-sea researches, in which I might hope that my own local 

 connection with Bristol would lead you to feel somewhat of a personal 

 interest. 



In the rocks that border the Avon on either side, the Bristolian 

 has one of the most characteristic examples of limestone that can be 

 anywhere found ; and he has only to go as far as the deep gorge of 

 Cheddar, in the Mendip hills, to find limestone cliffs yet more imposing 

 in height than St. Vincent's rocks ; or as far as Chepstow, to see, along 

 the Wye to Tintern Abbey, a still more varied and picturesque dis- 

 play of tfie same great rock-formation. Its material is sometimes dis- 

 tinguished as the mountain limestone, on account of the rugged char- 

 acter it imparts to the districts in which it prevails ; while it is now 

 more commonly known as the carboniferous (coal-bearing), because it 

 forms the basins or troughs in which the " coal-measures" lie. Now, 

 if you look at a geological map of England, you will trace this lime- 

 stone as a band lying obliquely northeast and southwest; beginning 

 in Northumberland, passing through Durham and Yorkshire, through 

 Derbyshire (where it forms the romantic scenery about Matlock), then 

 through the midland counties (where, however, it is generally covered 

 up by later formations), and then into Gloucestershire and South 

 Wales, where its relation to the coal-basins is most distinctly marked. 

 Speaking generally, this oblique band divides England into two great 

 areas : one to the nortliwest, in which the strata that have been brought 

 to the surface, by the crumpling action that has disturbed the crust of 

 the earth during its cooling, are older than the carboniferous lime- 

 stone ; the other to the southeast, in which the strata are newer. You 

 have not to go far from Bristol to see examples of both. As you pass 

 down the Avon, you observe a succession of limestone-strata lying 

 obliquely one beneath another ; and at last you come to an end of 

 these, and find that the next underlying rock is that Old Red Sand- 

 stone, of which the massive pier on the Somersetshire side of the sus- 

 pension bridge is built. And Dundry Hill, which is everywhere so 

 conspicuous, is formed at its lower part of Lias, and at its upper part 

 of Oolite, two later formations which were not deposited until after the 

 A Lecture given to the workingmen of Bristol, at the meeting of the British Asso-. 

 elation, August 28, 1875. 



