98 THE SHAUES-WITH-'BEEF.' [vol. lxxix, 



have taken place locally, while calcareous matter gradually 

 dissolved in the water-logged deposits. 



(2) Initial desiccation, possibly inaugurated or accompanied 

 by some elevation causing a motion of the solutions relatively 

 downwards. 



(3) Rhythmic precipitation of the concretionary limestone suite. 



(4) Stage of maximum desiccation. Regions, or levels, of low 

 pressure produced by contraction, along which supersaturated 

 solutions rapidly deposit veins of fibrous calcite (beef). 



(5) Desiccation and consolidation completed, with the precipi- 

 tation of any residual solutions which cemented and hardened the 

 marls. 



(6) The strata, including the concretionary deposits, faulted 

 and folded by earth-movements. 



Discussion. 



Dr. F. A. Bather said that, if Mr. Richardson were right, the 

 more obvious lithological character of the section could not have 

 influenced the succession of life. What, then, was the cause of the 

 repetition of faunas ? To answer that question we needed better 

 knowledge of the habits of ammonites, and we needed to trace 

 their migrations by equally careful collecting in other areas. But 

 a knowledge of ammonites would not suffice ; we must study the 

 other elements of the fauna (the flora was presumably be} r ond 

 reach). The researches of the Danish Biological Station showed 

 that similar faunal changes were taking place now, and that they 

 were frequently initiated by a disturbance of equilibrium in the 

 food-constituents of the life-assemblage. Those researches should 

 be studied by all who would solve these problems of stratigraphical 

 palaeontology. 



Mr. Gr. H. Plymeist enquired whether Mr. Richardson found it 

 possible to extend the application of the theory of precipitation by 

 diffusion, to the deposition of the ' beef '-beds and similar gypsum 

 sheets ; whether Liesegang's experiment might be considered on a 

 large scale, where calcareous waters overlying shales containing 

 sulphates would give banded precipitation of calcium sulphate. 

 These sheets then became contemporaneous, regardless of horizon. 



Prof. A. Hubert Cox remarked that lithological types similar 

 to those described by the Authors were well developed in the 

 Lower Lias along the Glamorgan coast. Individual bedding- 

 planes were stripped bare over wide areas along the shore, and 

 exceptional opportunities for their study were thus afforded. The 

 upper surfaces of the various limestone-bands presented certain 

 remarkable contrasts. Some of the surfaces had a persistent table- 

 like smoothness. Other bands of apparently identical lithology 

 showed very uneven surfaces, as if the beds were made up of 

 masses of irregular nodules. Despite the uneven surface, the 

 boundary between limestone and shale was quite sharp. His 

 explanation of the differences in the character of the limestone- 



