232 Reports and Proceedings. 



at least 3000 feet in Tertiary times, during whicli the Miocene 

 deposits were formed. The Tell Plateau was thus elevated at least 

 4000 feet, and the district north of the Lesser Atlas at least 1000 

 feet, the north face of those mountains probably marking a Post- 

 Tertiary line of fault of 3000 feet. This operation was followed by a 

 long period of denudation, and this by a Post-Tertiary depression, 

 which the author terms the " Sahara submergence"; after which the 

 land was re-elevated at least 3000 feet, but perhaps considerably 

 more. A gradual subsidence appears to be still taking place. 



Discussion.— Mr. "W. Boyd Dawkins considered an elevation of 3000 feet neces- 

 sary to allow of that migration of animals through Spain and Sicily to and from 

 Europe and Africa which took place in Pleistocene times; and this view appeared to 

 be confirmed on physical grounds by Mr. Maw. He believed that a great axis of 

 disturbance ran east and west along the course of the Mediterranean ; and to this the 

 strike of the beds observed by Mr. Maw was parallel. 



Mr. Bauerman called attention to the excellent drawing of a desert escarpment 

 exhibited by Mr. Maw. He said that this drawing perfectly represented what is to 

 be seen in every dry desert country, like the north of Africa or Arabia. In the latter 

 country the succession of the beds of JSeocomian and Tertiary age was similar to that 

 observed in Algeirs. He thought that the disturbances attributed by Mr. Maw to the 

 dissolving out of salt, were in reality due to the dissolving of gypsum. 



Mr. Davidson remarked that thirty years ago M. de Verneuil found many fossils in 

 the region to which Mr. Maw's paper related. These included a great Ojstrea, Tere- 

 hratulcE, and other forms which were both Miocene and Pliocene. 



Prof. Ramsay asked for information as to whether there was evidence of a great 

 sea having extended across the north of Africa at a comparatively recent period, as he 

 thought that this would explain certain ethnological phenomena. He was struck by 

 the difference of the elevation of that part of the Sahara visited by the author as 

 compared with that described by Prof. Desor. 



Mr. Prestwich considered the occurrence of recent shells at so great a height some- 

 thing quite new. The former French observers had referred to their occurrence on 

 the Sahara itself, and below the level of the sea. Subsidence appeared to be still 

 going on. 



Tiie Rev. Mr. Housman remarked that the eastern coast of Spain was still rising. 



The President observed that the existence of such tracts of high and absorbent 

 soil as those described might with even a moderate amount of rainfall account for 

 the supply of water to the Artesian wells with which the lower part of the Sahara is 

 dotted. He mentioned that Cardium edule and Buccinum gibbemlum had been found 

 in the Sahara by Desor, and that the latter had been considered identical with a shell 

 now found on the N.W. coast of Africa. 



Mr. IMaw briefly replied, and stated that the Haut Plateau referred to in his paper 

 was a tongue of elevated land, east of which, at all events, the desert stretched away 

 at or near the sea-level ; and this was undoubtedly submerged during the period of 

 depression. He thought that the sea also probably extended westward at the same 

 time, perhaps to the Gulf of Guinea. 



2. "On the Trimerellidas, a Palseozoic Family of the Palliobranchs 

 or Brachiopoda." By Thomas Davidson, Esq., F.E.S., F.G.S., etc., 

 and Prof William King, Sc.D. 



In this memoir the authors describe in detail certain Brachiopoda, 

 for which they propose to establish a distinct family, discuss the 

 characters and affinities of the family, and indicate certain geological 

 considerations which arise from their study of its members. The 

 first known species were described in 1853 under the names of 

 Obolus Davidsoni and 0. transversus, but in 1862 Mr. Billings de- 

 scribed an allied form as constituting a new genus called Trimerella. 

 With this Gotlandia of Dal I (1870) is identical. In 1871 Prof Hall 

 proposed the new genera Rhynoholiis and Dinobolus, and in the same 



