20 Murchison s Silurian System. 



and magnesian limestone ; 4. Lower red sandstone. The 

 first of these is described as occasionally presenting the 

 appearance of a greenish kind of marlstone included in beds 

 of red or green marls, of different degrees of tenacity; 

 sometimes the colour is almost a grass green, and at others 

 as white as chalk. It passes occasionally into a slightly 

 micaceous calcareous grit. It would be exceedingly difficult, 

 however, to give a mineralogical description of a formation 

 which Mr. Murchison traces throughout a large tract of 

 England, always appearing under some new character. The 

 salt springs at Droitwich, and other places, have procured 

 for it the name it bears. Salt springs occasionally occur in 

 other formations perfectly distinct. Mr. Murchison considers 

 the " Keuper" of foreign geologists is equivalent to the salife- 

 rous marls, and refers to a section made by Professor 

 Sedgwick and himself, on the continent, to prove the iden- 

 tity of the rock in the two remote localities, England and 

 Germany. 



The " Keuper," however, abounds in fossil plants as well 

 as animals ; and Mr. Murchison has never been able to detect 

 any trace of organic remains in the saliferous marls of 

 England. " The fossils of the overlying and underlying for- 

 mations in England being of marine origin, there is little doubt 

 that the red marl must also have been deposited beneath 

 the sea. In Germany and in France this inference is establish- 

 ed by the presence of marine remains, in the " Keuper," 

 " Muschelkalk," and " Bunter" sandstein, — the three prin- 

 cipal formations of the system ; the first of which, as before 

 mentioned, represents our saliferous marls. The second, or 

 great calcareous formation, has not yet been discovered in 

 the British isles ; and the third is the equivalent of the mas- 

 sive beds of central sandstones. The numerous brine springs, 

 as well as masses of rock-salt, which are contained in the red 

 marl, seems to offer additional proofs of the marine origin of 



