390 Br. James Croll — On Geological Time. 



Terehratula. It is so like the general shape of the species above 

 quoted, that I can hardly think it distinct ; however, the narrow 

 distinct sinus that runs down the larger valve appears constantly to 

 distinguish it from T. camelina. M. de Verneuil, who has seen our 

 specimens, pronounces the species distinct. T. pruniim, of Dalman, 

 from Gothland, is nearly allied, but still quite another species." 



Localities. — Cape Eiley, abundant. Cornwallis, Leopold, Griffith's 

 and Seal Islands. This species is also most abundant on Beechey 

 Island. 



Our figures on Plate X. are of immature specimens broken out of 

 a mass of young Atrypa phoca, from Beechey Island, brought home 

 by Dr. A. Horner of the "Pandora" (1875). We have since seen 

 and compared these with the large series in the Sutherland Collection, 

 Captain Penny, etc., and are satisfied from their gradations, that they 

 are all referable to the same species. Mr. Salter's and Prof. 

 Haughton's figures are of adult and aged specimens. We have 

 slabs from Beechey Island entirely made up of specimens of this 

 Brachiopod of all ages. 



EXPLANATION OF PLATE X. 

 Fig. 1. Strephodes {Lonsdalia ?) Aicstini, Salter, U. Silurian or Devonian ? Beechey 

 Island, Lat. 74^ 40' N., Long. 92° W. 



2. U. Silm-ian or Devonian ? Port Dundas, Lancaster Sound. 



3. Favosites polymorpha, Goldf. U. Silurian, Beechey Island. 



4. Gothlandica, Linn. sp. U. Siliu-ian, Beechey Island. 



5. Cyathophyllum Fickthornii, Salter. U. Silurian, Beechey Island. 



6. Salter. U. Silurian, Port Dundas. 



7. Alveolites arctica, H. "Woodw. U. Silurian, Beechey Island. 



8. Atrypa phoca, Salter sp. (young state). U. Silurian, Beechey Island. 

 a. front view, b. dorsal view, c. side view. 



II. — Cataclysbiic Theories of Geological Climate.^ 



By James Croll, LL.D., F.E.S., 



of the Geological Survey of Scotland. 



THE most important geological problem, and the one of all others 

 which at present excites the greatest attention, is the cause of 

 those extraordinary changes of climate which have taken place 

 during past ages. How are we to account for the cold and Arctic 

 condition of things which prevailed in temperate regions during 

 what is called the Glacial Epoch, or for the warm and temperate 

 climate enjoyed by the Arctic regions, probably up to the Pole, 

 during part of the Miocene and other periods? Theories of the 

 cause of those changes, of the most diverse and opposite character, 

 have been keenly advocated, and one important result of the dis- 

 cussions which have recently taken place is the narrowing of the 

 field of inquiry and the bringing of the question within proper 

 limits. 



At one time Lyell's theory of the relative distribution of land 

 and water was generally regarded by geologists as sufficient. It is, 

 however, now generally admitted to be wholly insufficient to ex- 

 plain the now-known facts, and the conviction is becoming almost 

 1 Eead before the Geological Society of London, May 8th, 1878. 



