578 DR. J. W. EVANS ON MECHANICALLY-FORMED [Aug. I9OO,. 



covered by a considerable thickness of false-bedded blown sands, 

 with occasional marine and numerous land-shells [36]. 



I am indebted to Mr. Chapman for the perusal of a paper by 

 Messrs. Rogers & Schwarz, describing the occurrence of extensive 

 false-bedded deposits near Cape Town (South Africa), formed almost 

 entirely of comminuted marine shells and containing in places the 

 bones of land-animals. The authors believe these beds to be of 

 reolian origin [41]. 



IX. The Oolites oe the Jurassic Period. 



Many writers have called attention to the resemblance between 

 the Jurassic rocks above the Lias and the deposits now forming 

 among the coral-islands of the tropics. 1 All the calcareous beds 

 afford evidence of the deposition of carbonate of lime from solution,, 

 either as a simple envelope covering organic particles, or in the form 

 of well-developed oolite-grains. False-bedding is often present, 

 especially where the rock is largely made up of oolite-grains or 

 fragmentary organic remains : see [45] p. 282. 



All the three classes, distinguished in this paper among granular 

 calcareous deposits accumulated in tropical or sub-tropical regions, 

 appear to be represented among the Jurassic limestones. 



Many of the Oolite-beds contain numerous uninjured shells of 

 mollusca, and we have every reason to suppose that these were 

 formed under the sea. The occurrence of calcareous mud between 

 the oolite-grains or other particles of which the rock is made up, 

 would point to a submarine origin, though it might sometimes be 

 present in beach-deposits. 



Elsewhere we have clear evidence that the beds were originally 

 a littoral formation. In 1862 James Buckman described the occur- 

 rence of reptilian eggs of elongated shape (Oolithes bathonicus) in an 

 obliquely laminated freestone a little below the top of the Great 

 Oolite at Cirencester [42]. He considered that the rock had been 

 accumulated on a 'widely shelving beach' or in a very shallow 

 sea. Rounded eggs resembling turtles' eggs were afterwards 

 described by Mr. Carruthers [43] from the Stonesfield Slates 

 (0. spkcericus)'. remains of turtles are found in the same bed. At 

 the present time turtles bury their eggs in the beach-sand just 

 above the high-water mark for spring-tides, and the crocodilia 

 select a similar position by the river-margin. The Stonesfield 

 Slates therefore, and the egg-bed of the upper portion of the Great 

 Oolite, represent gently-sloping beach-deposits, part at least of 

 which must have been raised above the reach of the waves. 2 In 

 other places, where the rock contains numerous broken shells larger 



1 See [46] pp. 16-21, and references there given. 



2 It is hazardous to argue from the habits of recent reptiles to those of the 

 Jurassic period ; but it is scarcely conceivable that a reptile, the young of which 

 breathe air from the time when they leave the egg, should lay its eggs where 

 they would be submerged at high tide. 



