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 resrard all shino^le-beds as evidence of grlacial 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. NatitJ'alist, iv, 560; Ramsay, Quar. Jour. Geo!. Soc, xh 

 197; Swansea Address; Sutherland {Quar. Jour. Geol. Soc, xxvi, 514; H. T. 

 Blanford, ib. 1875, 519; Daintree, Geol. Dist. Ballan Victoria., 1806, xi; C. D. Wal- 

 cott, Amer. Jour. Sci., Ill, xx, 222); Triassic (T. A. Conrad and H. Wiirtz. 

 1869; Jas. D. Dana, Atner. Jour. Sci. .,111, ix, 315, xvii, 330; Fontaine, Amer. 

 Jour. Sci., Ill, xvi, 236) ; Jurassic (Fontaine, loc. cit. ; Judd, Quar. Jour. Geol. 

 /S'oc.,xxix; Phil. J/ar/., xxix, 290); between Middle Cretaceous and Lower 

 Eocene (J. W. Dawson, Princeton Rev., March 1879, 284. Compare also Lycll. 

 Quar. Jour. Geol. -Soc. Lond., 11,280; 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. Rrp. 1857, O-^; 

 Geologist, 1860, 38); m the Cretaceous of India (A. C. Ramsay, Sn-asea 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. 



