HARDWICKE'S SCIENCE-GOSSIP. 



27 



and the prettiest spots to be found in Old England. 

 In many cases — perhaps in all — I believe these to 

 have been formed by the slow setting of the over- 

 lying rock-masses over the hollows left by the dis- 

 solving of the rock-salt beneath in the way I have 

 mentioned. I am told that in coal districts it is 

 very common for the upper rocks to settle over the 

 emptied seams, and to leave hollows on the surface. 



I have simply given you my own idea, to the best 

 of my recollection, of how rock-salt was formed. I 

 have heard others repeat their own, and if you like 

 will give it you, so that you may take them all for 

 what they are worth ; they have supposed a portion 

 of the sea to be separated from the rest by a bar of 

 sand, over which the ocean-waves every now and 

 then toppled to supply it with water. In this cut- 

 off sea, evaporation was going on, and a correspond- 

 ing precipitation of salt; the toppling water of 

 course supplying the place of that which had been 

 evaporated. It is certain that rock-salt contains 

 many of the same minerals as those usually met with 

 in sea-water; such as iodine, bromine, magnesia, 

 &c. So far, therefore, the argument is in favour of 

 a truly marine origin of salt. And the occurrence 

 of fish, reptiles, mollusca, &c, in beds of about the 

 same age as those of central Cheshire, indicates the 

 extension of a sea in which the water was fitted for 

 animal life. However, in either of these opinions, 

 the same principle lies at the bottom ; viz., that 

 rock-salt was precipitated from the surcharged 

 saline sea, and that evaporation by solar heat was 

 the immediate cause ! 



And now allow me to give you an idea of the 

 animals which lived on the dry-land surface at the 

 time when these important economical stores were 

 being laid up. First were several species of a great 

 frog-like reptile, or Batrachian. This type had 

 come into existence during the Carboniferous epoch, 

 although such primeval types seem first to have been 

 purely marine in their habits. During the Triassic 

 epoch, however, they certainly existed as land rep- 

 tiles. The largest of these great frogs was about 

 the size of a small ox ; their teeth are of a very 

 peculiar labyrinthine structure, and this character 

 is very persistent. Singularly enough, the feet- 

 impressions of these reptiles were found by geolo- 

 gists long before any of their remains had been met 

 with. Owing to their remarkable likeness to an 

 impression left by the human hand, the hypothetical 

 animal leaving them was named Cheirotherium, or 

 the "Beast with the hand." Another reptile, which 

 combined lower with higher reptilian characters in 

 a very extraordinary manner, was the Rhynchosaurus, 

 or "Beaked Saurian." It had the features of a 

 turtle, as regarded its horny bill, combined with the 

 characters of a true lizard. It seems to have been 

 web-footed, for in many parts of Shropshire and 

 Cheshire the sandstone flags are marked as thickly 

 with its webbed feet-marks, as is the margin of a 



clayey pond with those of ducks ! This reptile was 

 not nearly so large as the first I mentioned. The 

 Lahyriirfhodou, as that is now called, seems to have 

 haunted the shores of the Keuper Sea, for its foot- 

 marks are found at many levels. These are gene- 

 rally seen traversing ripple-marks, as though the 

 creature had passed over between tides. 



In America, the same geological formation is im- 

 pressed for more than a thousand feet in thickness, 

 with the crowded foot-prints of extinct birds. Every- 

 where you have evidence of slow subsidence — a 

 subsidence that was first compensated for by the 

 amount of material deposited over the subsiding 

 area. You may often trace for yourselves some- 

 thing of the habits of these singular and extinct 

 British reptiles, so well have the soft sandstones 

 done their duty fin recording what they felt and 

 saw ! Here the Labyrinthodons slowly lifted their 

 feet from the soft mud, from which there dropped 

 portions before they were next set down. Or you 

 may trace where they sluggishly squatted down, or 

 where their huge bellies trailed over the soft ooze! 



But by far the most interesting of the in- 

 habitants of the dry land were small warm- 

 blooded animals, belonging to the lowest divi- 

 sion of the class — the Marsupials, or "pouched 

 animals." These are now inhabitants of Aus- 

 tralia, Tasmania, and North and South America 

 — their isolated distribution proving their vast an- 

 tiquity. In the times intervening since they first 

 made their appearance, species belonging to this 

 group have lived in various parts of the world. 

 That to which 1 am alluding is very remarkable, as 

 being probably the first warm-blooded animal which 

 appeared on the earth ! Its name is Microlestes, or 

 the " little thief," so called on account of its in- 

 sectivorous habits, as indicated by its teeth. This 

 little creature — for it was not much bigger than a 

 rat — preyed on the insects which then abounded in 

 the pine-forests, or amid the thickets of fern and 

 club-moss. 



In a bed of later date, formed at the close of the 

 Triassic epoch, and now termed the Rhsetic forma- 

 tion, the strata are crowded with fossil insects. 

 Erom this time forth the geologist never loses sight 

 of the mammalia, and many deposits of later date 

 contain a considerable number of species. In its 

 fossil state, the Microlestes has been found both in 

 Germany and England. However, time fails me to 

 say what I have heard of the strange creatures 

 which lived elsewhere, during the epoch when I 

 was born. It is more than probable that the nu- 

 merous gigantic birds, whose foot-prints are found 

 in the Connecticut Valley, had reptilian affinities— 

 just as, during the Oolitic period, the reptiles had 

 ornithic, or bird-like affinities. 



In South Africa there existed a peculiar group 

 of reptiles termed Dicynodonis, from the peculiar 

 walrus-like characters of their tusks or teeth. They 



c2 



