578 



SCIENTIFIC RECREATIONS. 



mollusca, and the gradual approach to the Crustacea, but no terrestrial 

 animals have been discovered. We may take it for granted then that the 

 Old Red Sandstone and Devonian systems are different the former being 

 found in Scotland and parts of England, and formed of deposits in fresh or 

 brackish water, while in the Devonian system the marine deposits are corals, 

 and all the indications of ocean life, separated from the great inland lakes 

 by a range of hills. Neither of the terms (Old Red Sandstone or Devonian) 

 limit geographically or descriptively the formations of this system. All the 

 rocks are clearly distributed between the Silurian and the Carboniferous. 

 The invertebrates in this last system have not developed very much, but corals 

 are very abundant, and fish of some armoured species are plentiful and 

 curious, while the Crustacea were enormous. 



Fig. 659. Palaeozoic Fish. Trilobites, Rrachiopods, Coral and Graptolite. 



We now arrive at the most important of all the rock formations, the 

 one to which we owe our national prosperity we mean the COAL System. 



THE CARBONIFEROUS FORMATION. 



While the foregoing depositions were being made the earth was still 

 undergoing changes. The sandstones were deposited, and the corals making 

 use of the lime carried into the waters began to build and form masses of 

 limestone under the sea, pushing back the water and changing the forms 

 and positions of land and water. All this went on apparently very quietly 

 volcanic action was not very frequent the water was warm. But sometimes 

 earthquakes would heave up the submarine formations into mountains, and 

 therefore we find the fossils of the tiny sea-animals on the hills. Extensive 

 swamps were formed by partially retreating sea-water, and their vegetation 



