328 GEOLOGY OF THE ISLE OF AVIGHT. 



covered last year in the Wealden sands at Has- 

 tings, and sent up to the Geological Society. A 

 similar cast has been obtained from the Wealden 

 sand in the cliff in Brixton Bay, and is in my pos- 

 session. This specimen is a solid tripartite mass 

 of fawn-coloured sandstone ; the middle process 

 is fifteen inches, and the two lateral projections are 

 twelve inches in length ; the greatest thickness is 

 six inches ; the processes are laterally compressed 

 and rounded at the extremities, and united to one 

 common base. As the origin of these singular 

 concretions is very problematical, every specimen 

 should be preserved ; and if several occur on the 

 same bed of sand, their relative position should be 

 carefully ascertained.* 



Ancient ripple-marks. — Connected with this 

 subject are the ripple-marks so often pervading 

 extensive surfaces of sands, sandstones, and clays, 

 in sedimentary deposits that have been formed 

 on sea-shores, or along the banks of rivers, or in 



* The method adopted to obtain impressions from engraved monumental 

 brasses, namely, the placing of tough thin paper over the surface of the in- 

 scription or effigies, and rubbing it freely with the black composition termed 

 " heel hull," which adheres to the parts in relief, but leaves the cavities 

 white, will be found convenient for obtaining an accurate plan and outline of 

 the imprints on the sandstone. This process is also applicable to anj fossil 

 that lias a surface flat and firm enough to bear the friction when covered by 

 the paper. I have often taken in a few minutes, imprints of the plates of 

 turtles, scales of fishes, &c. sufficiently distinct to exhibit the general cha- 

 racters of the surface of the specimens. 



