TRANSACTIONS OF THE SECTIONS. 69 



pendently of this, however, it was asked if mica, such as it occurs in mica-schist, might 

 not often rather be the result of the physical condition of other mineral combinations, 

 than those forming well-characterized micas ; whether those combinations were definite' 

 minerals, or only indefinite mixtures of silicates of alumina with other silicates? 



Finally, it was stated as the general result, that no one could examine the district 

 without arriving at the conclusion, that as perfect mica-schist, gneiss, &c. as can be 

 found in any so-called primitive district, has been produced by the metamorphosis of 

 earthy clay-slate by the granite, and without being convinced that all schistose rocks, 

 even the most crystalline gneiss, had a similar metamorphic origin. 



On some Fossil Fishes from the Strata of the Moselle. By J. E. Lee. 



On an Elephant's Grinder from the Cerithium Limestone. By J, E. Lee. 



On the Time required for the formation of " Rolled Stones." 



By M. MOGGRIDGE. 



The uncertainty which prevails as to the period required for the reduction of rough 

 stones to the condition of " rolled " pebbles, has led me to make the following obser- 

 vations at a place where the time occupied in that process is susceptible of proof —at 

 least as regards the maximum. ' 



Limeslade Bay is the second inlet of the sea to the west of the Mumble Point in 

 Glamorganshire. It runs into the land to the depth of 206 yards, 56 of which are 

 covered by shingle. The width at the mouth is 80 yards ; and in the broadest part 

 a little below the bottom of the shingle, ] 03. Hard firm sand of an average width of 

 20 yards occurs from low water to the shingle ; on each side of which are large and 

 rugged rocks filling up the rest of the inlet. It would not appear therefore that the 

 action of the sea can be peculiarly violent here, more especially when we consider 

 that the general bearing of the little fiord is N. 10° E. and S. 10° W., the prevaihno- 

 winds being westerly, and the western promontory somewhat overlapping: the 

 eastern. ° 



The sea occupies the southern end, and at the northern is the Mumble hill fcarboni- 

 ferous limestone), through which, nearly in continuation of the line of the inlet, runs 

 a lode of dark peroxide of iron, first opened at this end in 1846, the refuse stones 

 being thrown into the little bay already described, somewhat below high-water mark. 

 ;• Of these stones the smaller are now generally completely rounded ; while some, 

 which from their size or configuration remained stationary, have their under sides 

 unaltered, i. e. rough as when quarried, and the exposed portions ground down and 

 rounded, presenting in fact the appearance of large "rolled stones " split through the 

 middle. I have measured (July, 1856) two of the latter. 



No. 1 is of calcareous spar; the underside flat and rough, 1 ft. 1 in. by 1 ft. 1 in, 

 over the rounded part 2 ft. '' 



No. 2 is limestone ; under side 1 ft. 2 in. by 1 ft. 4 in., over 2 ft. 



The efiects produced by the attrition appear to be irrespective of the toughness or 

 resisting power of the material ; calcareous spar, carbonaceous limestone, and the dark 

 peroxide of iron being found occasionally in the same stone, and equally worn down. 



The general result to be deduced from the above may be thus stated ;— that on a 

 beach not more than usually exposed to the action of the sea, ten years sufficed for 

 the formation of "rolled stones." 



On the Skin and Food of Ichthyosauri and Teleosauri. 



By Charles Moore, F.G.S. 



In clearing specimens of the former genus dark patches of matter have been 



frequently seen, m association with which thousands of minute black hooks may be 



noticed by the aid of the lens. These have been supposed to be portions of the outer 



of the Ichthyosaurus covered by the hook-shaped processes referred to. It was 



stated by Mr. Moore that out of twenty-three saurians in his museum he had traced 



these black patches in not less than sixteen; but that as in every instance they were 



