382 Corresjjondence — Festina Lente. 



nized groups. Many Palaeozoic forms are in a different case. The 

 orifices seen on the surface are not, in many instances, the mouths 

 of the cells, but those of what the authors call vestibules beneath 

 which the true cell-mouth is concealed. For these types they pro- 

 pose to found a new suborder uader the name of CKYPTOSTOBIA.TA, 

 and characterized by having the zooecia subtubular, or, in section, 

 slightly angular, and the orifice surrounded by a vestibule or other- 

 wise concealed. The families referred to this group are the Ceramo- 

 poridee, Ptilodictyidse, and Arcanoporidse. 



8. " On the Cause of the Depression and Ee-elevation of the land 

 during the Glacial Period." By T. F. Jamieson, Esq., F.G.S. 



The author commenced by noticing the theory advanced by Adhemar 

 and Croll, according to which the submergence was due to the effect 

 of a polar ice-cap causing a displacement of the earth's centre of 

 gravity and thereby drawing the ocean towards the ice-covered 

 pole, and proceeded to show that this theory is opposed to the geolo- 

 gical evidence, according to which the amount of submergence has 

 been unequal in adjacent areas and along the same parallels of 

 latitude, showing that the movement has been in the land and not 

 in the sea. The facts of submergence also prove that no such cap 

 of ice could have existed at the time in the northern regions. 

 Sundry other objections were also pointed out. The author then 

 went on to state his own hypothesis, which is to the efiect that the 

 depression of the land was caused by the weight of ice laid upon it, 

 and the re-elevation by the disappearance of the ice. The amount 

 of depression would depend partly on the weight of ice and partly 

 on the elasticity or yielding nature of the ground beneath it. He 

 then proceeded to consider what was the weight of ice that probably 

 existed, and referred to the elastic and flexible nature of the earth's 

 crust, as evinced by earthquakes, etc. 



He further considered the relation of time to pressure, and touched 

 upon the probable rate of subsidence, which he supposes to have 

 been very slow and gradual. The recovery of level, he thinks, would 

 be very gradual, and probably, in most cases, not complete. 



He next proceeded to show bow his hypothesis is borne out by an 

 appeal to geological evidence in various countries, taking England, 

 Ireland, North America, and Greenland as examples. He further 

 pointed out its application to the facts connected with the loess beds, 

 fjord latitudes, and lake-basins, and concluded with some observa- 

 tions on the remarkable connexion between glaciation and submer- 

 gence in all countries. 



THE MOON'S ACTION ON THE EARTH. 

 Sir, — I dare say your readers will have been much interested 

 lately by Professor Ball's new speculations regarding the moon's 

 action on the earth, and especially in the creation of geological 

 changes on its surface by it. His theory purposes to establish 

 gigantic tides in the far-off history of the Earth, upheaved by a 

 closer approximation of the moon, and creating thereby a tremendous 



