ON A PIECE OF LIMESTONE. 169 



Postponing for the present the more detailed inquiry into the 

 origin of our own Limestone, of which this general survey is the pre- 

 lude, I pass on to the Permian formation, which rests upon the Car- 

 boniferous, and has been upheaved with it, having been deposited pre- 

 viously to the general disturbance that closed the Palseozoic (ancient 

 life) period. Of this Permian formation there are few traces in our 

 part of England ; but it has a much greater development in the north, 

 and to it belongs that remarkable bed of Magnesian limestone which 

 comes to the surface in Northumberland and Durham. It is of this 

 stone (selected on account of the durability it has shown in York Min- 

 ster and other old buildings) that the Houses of Parliament are built. 

 Now, although very few fossils are found in this rock, yet I believe 

 that most geologists would agree that it was originally formed, like 

 limestones generally, by the growth of corals, shells, etc., which sepa- 

 rated the carbonate of lime from the sea-water they inhabited ; its 

 subsequent conversion into magnesian limestone having been proba- 

 bly effected by the infiltration of water in which magnesia was dis- 

 solved. In the Eozoic limestone of Canada, I have myself frequently 

 met with veins of dolomite (magnesian limestone), w^hich retain the 

 general arrangement characteristic of the original shell, although its 

 minute structure has been obliterated by this metamorphic action. 



Passing on now to the Secondary or Mesozoic (middle life) series, 

 we find that although the Trias, which is the oldest member of it, is 

 represented in England by sandstones alone, there is an important 

 bed of limestone in Germany called the Muschelkalk (shell-limestone), 

 which is interposed between the lower and the upper New Red Sand- 

 stones. This bed derives its name from the fact that it is obviously 

 formed by an aggregation of shells, mingled with other fossils, among 

 which the beautiful Lily Encrinite is one of the most abundant. In 

 the Lias, which overlies the New Red Sandstone, a considerable por- 

 tion of lime is generally mingled with the clay deposits of which this 

 formation is principally composed ; and some of its beds, especially 

 on the northeast of Yorkshire, are almost entirely calcareous. If you 

 walk along the shore between Saltburn and Whitby, and examine the 

 blocks wiiich have fallen from the lias cliffs above, you wnll find them 

 to be almost entirely made up of fossils ; among which Belemnites 

 conical chambered shells, with solid calcareous " guards," which be- 

 longed to animals resembling cuttle-fishes are specially abundant. 

 And here, as elsewhere, the calcareous matrix in which the fossils are 

 imbedded, though sub-crystalline in some parts, is obviously made up 

 in others of fragments of shell, etc., ground down by the action of the 

 sea in which the deposit was formed. The Lias abounds in the neigh- 

 borhood of Bristol, and is exposed in many railway-cuttings. These, 

 when in progress some forty years ago, yielded many valuable fossils, 

 especially skeletons of the great Fish-Lizards, which you will see in 

 the Museum of the Bristol Institution. In this neighborhood, also, 



