10 A Period in the History of our Planet, 



oceans ; in fact, the more anomalous forms, as the Orthocera- 

 tites, have already vanished, and only the beautiful spirally- 

 coiled ammonites and nautili retain their place in the ocean, 

 clad in their coat of mail, while all around them are naked. 

 The most various forms of all families of shells and echini 

 peopled the sea and coasts, whilst the most beautiful polypi 

 and stalked echinodermata occupied its cliffs and banks, and 

 various kinds of tortoises, with gigantic lizards, allied to the 

 crocodiles, which often remind us of the present huge pachy- 

 dermata of the tropics, followed their prey upon the shores. 



And what collections of crabs, dragon -flies, beetles, worms, 

 and other forms of articulated animals has not the untiring 

 zeal of inquirers brought to light ! Tropical vegetation also 

 had taken root upon the dry land, although not to such a 

 great extent as in the preceding period. In fact, sea algse 

 and the strange-looking Cycadeae, with a few coniferae, are the 

 sole witnesses that the vegetable creation, although overpoised 

 by the animal, was not entirely suppressed. 



The domes and ridges of the Jura arose as strong dykes, 

 and formed, along with the previously elevated mountains, the 

 shores of the seas whose larger inhabitants, visible to the naked 

 eye, lie included in the masses of carbonate of lime which, on 

 account of their pecuHar constitution, were formerly regarded 

 as the purest examples of continuous deposits from water con- 

 taining lime. I say formerly, because now, by the help of the 

 indefatigable Ehrenberg, we see in those formless deposits of 

 the chalk most astonishing collections of innumerable micro- 

 scopic animalculse, whose calcareous shells, heaped up in mea- 

 sureless quantity, constitute immense ranges of mountains. 



But apart from these organisms, invisible to the naked eye, 

 what important progress is made towards the perfection of the 

 types which now people our earth. The radiated animals free 

 themselves more and more from the ground to which they 

 were attached during the earlier epochs; the encrinites in 

 their various forms, which still inhabited the Jurassic seas, 

 give ground, and the varied forms of sea- stars, whose arrival 

 was hardly announced by a few feeble indications in the lime- 

 stones of the Jura, take for the most part their place. On the 

 sequence of the families of molluscous animals and their geo- 



