568 Reviews — Oolite from Betldehem, Pennsylvania. 



Lower Coal-measures in the Kent Coal-field. From his studies of the 

 fossil flora of the region, Dr. Arber has been unable to recognize the 

 existence of the older Coal-measure Series, whereas the author states 

 that the occurrence of Lingula, Orbictdoidea, and Productus con- 

 clusively proves the opposite view, he being also of opinion that 

 a fauna furnishes more reliable data as "determinants of the age of 

 the beds" than the flora. The palseontological evidence is considered 

 to support Marcel Bertrand's theory "of a formerly continuous coal- 

 field stretching from South Wales on the west, through Bristol and 

 Somerset into Kent, and thence eastwards to the Pas-de-Calais of 

 Northern France and Belgium ". A plate of fossils and diagrammatic 

 sections of the various borings add to the great interest of the 

 memoir, among the former being illustrations of Prestwichia anthrax, 

 different forms of Anthracomya, Naiadites carinata, Lingula mytiloides, 

 Orbictdoidea nitida, Productus scabriculus, Ccelacanthus elegans, etc. 



R. B. K 



V. — A peculiar Oolite from Bethlehem, Pennsylvania. By 

 Edgar T. Wherry. Proc. U.S. Nat. Mus., vol. xlix, pp. 153-6, 

 pis. xl, xli, 1915. 



rnHE oolite described occurs in magnesian limestone of Upper 

 1 Cambrian age, and is chiefly remarkable for the fact that, 

 except in the centre of the blocks formed by bedding and joint-planes, 

 the grains are divided equatorially into upper light and lower dark 

 portions. They are composed of dolomite of purer consistency than 

 the matrix, and the darkness of the lower halves is due to 

 carbonaceous matter. 



The author's explanation is as follows : — " When the ooids [oolitic 

 grains] were first formed they no doubt consisted of aragonite, 

 whereas the matrix was dolomite-mud. Mixed with the aragonite, 

 in varying amounts in the different concentric layers, was the 

 carbonaceous pigment. After the solidification of the sediment into 

 rock and the development of joint cracks (but before the uptilting of 

 the beds) waters penetrated along these cracks and along the bedding 

 planes. Since aragonite is more soluble than the dolomite of the 

 matrix, it dissolved away, leaving behind the carbon and the nuclei — 

 sand grains and bits of kaolin — in some cases stripped of all con- 

 centrically deposited aragonite, in others still retaining a few layers. 

 These settled to the bottom of the cavities in heaps, the shapes of 

 which varied with the sizes of the nuclei and the stage of solution 

 process at which they fell into the masses of carbon powder. 



"At some later period water again traversed the rock, but this 

 time conditions were favourable to deposition instead of solution, and 

 secondary dolomite filled up all openings in the rock, tension and 

 joint cracks as well as the holes left by the removal of the ooids . . . 

 The secondary crystallization took place so slowly and quietly that 

 the heaps of carbonaceous dust were not disturbed, but merely 

 enclosed by the crystal grains, and their shapes preserved." 



