48 PICTURESQUE SKETCHES 



ing, to observe that these species were not only 

 absent, but that their place was supplied by other 

 groups of animals analogous to them, having similar 

 habits, but not identical in specific character. 



Thus the place of the less highly organized of the 

 common shell-fish, such as the muscles, the oyster 

 tribe, and the like, was properly filled by numerous 

 and varied forms allied to Terebratula (a lower group) ; 

 while the numerous groups of flesh-eating Gasteropo- 

 da (the Murex, the cone, the volute, the cowry, 

 and many others) were equally well represented by 

 innumerable orthoceratites (animals of higher organi- 

 zation), which then swarmed in the seas. 



No doubt the appearance of these ancient seas 

 would have appeared strange to the eyes of the 

 naturalist, could an inhabitant of the world in its 

 present state have become acquainted with the 

 mysteries of the ocean's deep abysses at that time. 

 With something of resemblance in the reefs and 

 islands of coral rising gradually to the water's edge, 

 as the coral polyp toiled and laboured from day to 

 day and from year to year, there would yet be much 

 more of difference both in the shallows and depths of 

 the ocean. The former sometimes with a sandy, but 

 more frequently a muddy bottom, would be peopled 

 with countless myriads of those unsightly animals, 

 the trilobites, swimming near the surface of the water 

 with their backs downwards, looking out constantly, 

 and sinking at the slightest approach of danger from 

 beneath; while the remains of successive generations of 

 these creatures, mixed with mud and sand, would rapid- 

 ly form beds sometimes of great extent. From amongst 

 such beds, or attached to the solid rock, would be 



