202 GEOLOGY. 



formation, but, if so, they have been denuded by the ac- 

 tion of water. 



292. Devonian System in Europe. Devonian rocks are 

 found in most of the countries of Europe. In Germany 

 they cover a larger space than the Silurian. This sys- 

 tem is very marked in England, and also in Scotland, 

 where the genius of the lamented Hugh Miller has given 

 it a deep but melancholy interest. In Russia, south of 

 St. Petersburg, it covers an area of 150,000 square miles. 

 In connection with the Devonian of Russia, I will men- 

 tion an interesting example of geological investigation. 

 It was doubted for some time whether the red sand- 

 stone of Devonshire was of the same period with that 

 of Hereford, because the strata of Devon contained cer- 

 tain shells which were not found in the rocks of Here- 

 ford, while the latter contained fishes that were not found 

 in those of Devon. Sir R. Murchison settled this ques- 

 tion by finding in Russian strata both he shells of De- 

 von and the fishes of Hereford. You see what this shows 

 that the rocks in Russia, in Devon, and in Hereford 

 belong to the same epoch, and that the fact that the 

 fishes and shells were not found together in both Devon 

 and Hereford was owing to some locarcauses. 



293. Coral Formations. I have stated in 290 that 

 the strata of this age first laid down were limestones. 

 The corals had a great agency in providing material for 

 these. Indeed, the upper Helderberg period was, Pro- 

 fessor Dana states, " eminently the coral-reef period of 

 the Palaeozoic ages." Near Louisville, Kentucky, at the 

 Falls of the Ohio, there is a grand display of the lime- 

 stone of this period, very much like a coral reef of the 

 present time. At all seasons when the water is not high 

 a series of ledges is exposed, and the softer parts of the 

 rock -having been worn away, the harder corals stand out 

 in bold relief, and many of them branch out precisely as 

 if they were living. There are honey-comb, cup-shaped, 

 star-like, and other forms mingled with the joints, stems, 



