HARDWICKE'S SCIENCE-GOSSIP. 



221 



latest improvements for showing an intermittent 

 light. 



Returning to the western side of the island before 

 referred to, one of the most interesting examples of 

 ripple marking meets the view it is possible to 

 conceive ; in fact, so prominently defined are the 

 ridges, that it might be more correctly termed wave 

 marks. For a space of about 20 yards square the 

 surface of one bed is exposed, and the eye looks down 

 upon what may not be inaptly termed a petrified sea. 

 It requires no very great stretch of imagination to 



the action of the waves in the manner indicated 

 above. 



It has been pretty generally accepted that compact 

 and thickly bedded limestone indicate conditions of 

 deep clear water at the time of deposition, and that 

 the disturbance caused by shallow water was not 

 favourable to its production, but of late there have 

 not been wanting attempts to prove that these features 

 were not strictly essential ; the evidence furnished 

 by this particular bed is therefore exceedingly 

 valuable, as going to some distance to prove that a 



Fig. 141. — Atnfilcxus 

 coralloides. 



Fig. 142. — Head and tail of 

 Trilobite (Phillipsia). 



Fig. 143. — Pleurotomaria 

 carina t a. 



Fig. 144. — Product us 

 punctatus. 



Fig. 140. — Stem of Encrinit?. 

 Characteristic Fossils of the Carboniferous Limestone. (From Taylor's " Common British Fossils.") 



conceive the idea, that the waves had been turned into 

 stone as they approached the coast in a west north- 

 westerly direction, and that you were now looking 

 down upon a palaeozoic sea. 



The rock is a compact thickly-bedded sub-crystalline 

 limestone, and when viewed microscopically has a 

 granular appearance. It is almost, if not wholly, 

 made up of organic remains, consisting of foraminifera, 

 minute ossicles of encrinites, fragments of what 

 appear like tests and spines of echinoderms, and 

 small bodies resembling minute corals. All are fairly 

 well preserved, but nevertheless exhibit to some 

 extent the effects of attrition to which they have been 

 subjected, as occupants of a plastic mass encountering 



limestone of undoubtedly marine origin can be and has 

 been formed in water sufficiently shallow to receive 

 the impress of the waves as they rolled over the 

 limey floor or beat upon an ancient coast. 



The bed immediately succeeding the above de- 

 scribed is also built up of similar organisms, but the 

 frail forms of foraminifera are more plentifully dis- 

 tributed than before. Their presence appears to 

 indicate that the water had become sufficiently deep to 

 place the bottom out of the influence of the grinding 

 power of the waves, and as they are examined the 

 truth of Byron's line — 



"The dust we tread upon was once alive !" 



forces itself upon us. It points also to the subsidence 



