kinds, echintjderms, insects, wood and corals, are met with in its 

 layers. The insects,— which, according to Westwood, belong to 

 no less tlian 24 families, and comprise both wood-eating and 

 herb-devouring beetles, grass-hoppers, dragon-flies, and may-flies, — 

 together with the wood, were, doubtless, brought down by the 

 rivers which flowed into the sea; while the corals owe their 

 presence to tlie extension of its waters southwards, enabUng 

 the products of warmer cHmes to push up towards the north. 



iVmongst the mollusca the Ammonites hold the first place. 

 Chambered shells of great beauty, which have their counterpart 

 in the Nautilus of the present day, they vary very much in 

 shape, and are so distinct, that tliey have been used to designate 

 zones of life in describing the Liassic strata, each zone having 

 its distinct Ammonite as a characteristic feature ; and, although 

 this cannot altogether be relied on, — some Ammonites being 

 found in more zones tlian one, and not always in the zones 

 to which they give their name, — yet the fact of different species 

 being found in succession, one above the other, as the higher 

 beds appear, bears strong testimony to the vast period of time 

 that must lipve elapsed during th^ formation of these strata. 

 We have only to call to niind h ;w slowly forms of molluscan 

 life, (and we may say the same of life generally,) die out now, 

 and are replaced by otliers, to appreciate this. 



Taking an illustration near our own time, we find that, 

 out of the shells in tha Norwicli Crag at the top of the 

 Pliocene period in the Tertiary age, 85 per cent exist at the 

 present day ; and yet, between that period and our own, lies 

 the whole of the Pleistocene and Glacial age, during which 

 the iMammoth, the cave Bear and the Hya.'na, the woolly 

 Rhinoceros, the great Irish Elk, and other animals, appeared 

 on the scene and passed away ; hunted to death for the most 

 part by man. 



It is however in the Saurians that the great interest of 



