178 SPARKS FROM A GEOLOGIST'S HAMMER. 



known as the Molasse, seems to be but an older bed of gla- 

 cier pebbles, extremely similar to those accumulated upon 

 the existing surface along the slopes and flanks of the Alps. 

 Mr. Croll, a distinguished Scottish geologist, is of the opin- 

 ion that most of the shingle formations, through the whole 

 series of rocks, are but ancient glacier accumulations. If 

 so, the evidences of oft-repeated epochs of glaciation are 

 abundant and familiar. The conglomeritic deposits of the 

 Coal Measures are regarded by Croll as of this character, 

 while the coal-beds intervening between the fragmental 

 strata are regarded as the records of interglacial periods. 

 These phenomena of alternating coal-beds and fragmental 

 strata are generally explained on the hypothesis of alterna- 

 tions in the relative levels of land and sea, not necessarily 

 accompanied by great changes of climate. Personally, I do 

 not accept, as yet, Mr. Croll's view. I consider it a plain 

 error to regard all shingle-beds as evidence of glacial ac- 

 tion. Pebbles imply attrition, long continued attrition; 

 but the force of moving water is adequate to the produc- 

 tion of beds of pebbles. This is exemplified upon the shores 



222) ; PERMIAN (Amer. Naturalist, iv, 560; Ramsay, Quar. Jour. Geol. Soc., xi, 

 197; Swansea Address; Sutherland (Quar. Jour. Geol. Soc., xxvi, 514; II. T. 

 Blanford, ib. 1875, 519; Daintree, Geol. Dist. Ballan Victoria, 1866, xi; C. D. Wal- 

 cott, Amer. Jour. Sci., III, xx, 222); TBIASSIC (T. A. Conrad and II. Wurtz, 

 1869; Jas. D. Dana, Amer. Jour. Sci., Ill, ix, 315, xvii, 330; Fontaine, Amer. 

 Jour. Sci., III, xvi,<36) ; JURASSIC (Fontaine, loc. cit. ; Judd, Quar. Jour. Geol. 

 Soc., xxix; Phil. Mag., xxix, 290); between MIDDLE CRETACEOUS and LOWER 

 EOCENE (J. W. Dawson, Princeton Rev., March 1879, 284. Compare also Lyell, 

 Quar. Jour. Geol. Soc., Lond., ii, 280; Travels in N.America, 1st Visit, ii. 68; 

 M. Tuomey, Geol. Ala., 116; W. B. Rogers, Proc. Boston Soc. Nat. Hist., xviii, 101 

 seq. 1875, Amer. Jour. Sci., Ill, xi, 61); in the English CRETACEOUS (Godwin 

 Austen, Quar. Jour. Geol. Soc., xiv. 262, xvi, 327; British Assoc. AV;>. 1857, 62; 

 Geo'ogist, 1860, 38); in the CRETACEOUS of India (A. C. Ramsay, Swansea Ad- 

 dress); a cold period at base of Eocene (Nature, July 10. 1879, 258); in the 

 FLYSCH of Switzerland (Lyell, Principles); in the MIOCENE (Gastaldi, Mem. 

 Acad. Sci,, Turin ii, xx; A. C. Ramsay, loc. cit ); on CroH's extension of the 

 idea to the Coal Measures, see Climate and Time, 296-8, and ch. xxvi. Opposed 

 to the doctrine of recurrence of glacial periods, see A- R- Wallace in Island 

 life. 



