152 



The New Red Sandstone of the Triassic System, which 

 underlies the lowlands of Tees-side, contains no local organic 

 remains of enough importance to be considered here. It 

 may be remarked in passing, however, that these rocks are 

 composed of sand formed under desert conditions, and pro- 

 bably blown by the wind into lakes saturated with salt, now 

 lying at a depth of nearly two thousand feet. Succeeding 

 the Triassic rocks comes the well-known Lias, but the change 

 of geographical condition which first supervened, is indicated by 

 a set of beds termed the Rhaetic (after the Alps of that name 

 where they are characteristically developed), containing a 

 few stunted marine fossils. Of these the most important is 

 the shell known as Avicula contorta, remarkable for its wide 

 distribution in various parts of Eastern, Western, and Southern 

 Europe, of course on the same geological horizon. The teeth 

 of Sharks are of frequent occurrence, and are of interest from 

 the fact that their nearest living representative, is the Port 

 Jackson Shark of the Australian Seas. 



With the Lower Lias, so picturesquely developed on the 

 scars at Redcar, Saltburn, and Robin Hood's Bay, we are 

 introduced to a rich and varied fauna, the statistics of which 

 can be gathered from Table 2. On comparing the fauna 

 of the Lias with that of the Cleveland coast, we find that the 

 number of species in the former is greater than in the latter. 

 But as we have seen the full number of living species is still 

 far from being known, if these could be enumerated the 

 total would probably be greater than that for the whole of 

 the Lias. 



This comparison would be misleading, however, if we do 

 not bear in mind the fragmentary character of the fossil 

 faunas. This imperfection of the geological record is owing 

 to the circumstance that only animals which secrete hard 

 parts leave any remains in the stratified rocks, such soft- 

 bodied organisms as jelly-fish, worms, and sea-slugs, disappear 

 altogether, and many other animals must, though possessing 

 hard parts, decay away before they can become petrified. 

 Joining these considerations with the long period of time 

 during which the Lias was laid down, we may feel sure that 

 animal life was more abundant in those days than it is now, 

 as far as the immediate district is concerned. 



