376 Mr. Lyell on the Boulder Formation^ 



some granitic boulders are floated in ice from the distant 

 shores of Labrador into the Gulf of St. Lawrence, while 

 other large fragments of rock, together with much gravel and 

 sand, are firmly frozen into ice and carried down every winter 

 by various rivers into the same gulf. As the part of Canada 

 where this drift is now forming corresponds in latitude to 

 that of Norfolk, the adoption of this theory of ice-drift does 

 not of necessity require us to assume the former existence of 

 a colder climate than that now prevailing in North America. 



Dr. Mitchell, in a paper on the Drift of Norfolk, Suffolk, 

 &c., (Geol. Proc, vol. iii., p. 5) has suggested that the ma- 

 terials have been in great part derived from the destruction 

 of strata which once occupied the site of the German Ocean. 

 This conjecture is, I think, by no means improbable, and we 

 are often too prone, when speculating on the original site of 

 travelled boulders, to refer them exclusively to the places 

 where similar substances happen now to be exposed above 

 water, whereas they may often have come from a neighbouring 

 refjion now submerged. The island of Helifjoland for ex- 

 ample, about forty miles off the mouth of the Elbe, has been 

 wasting away for centuries, and in time will probably disap- 

 pear. Its cliffs, from 100 to near 200 feet high, composed 

 of marl and marlstone of the new red sandstone formation, 

 might supply stony fragments and red mud, which if stranded 

 by ice or other agency on the adjacent coasts of Holstein, 

 Bremen, or Friesland, would differ entirely from the rocks 

 occurring there in situ, or from any rocks met with nearer 

 than parts of Hanover, situated 100 or 150 miles in an op- 

 posite or eastern direction. We ought always, therefore, to 

 bear in mind, that fragments of chalk, green sand, oolite, and 

 lias, imbedded in the drift of Norfolk and other counties, 

 may not have come from the westward where those forma- 

 tions now crop out, but possibly from the N.N.E,, like the 

 erratic blocks, if some of these be really of Scandinavian 

 origin. 



The association of stratified drift'with unstratified materials 

 or till, a general character of this formation in Sweden and 

 Scotland, as in Norfolk, has been already attributed to the 

 possible cooperation of ice and currents of water (see p. 348). 



DISTURBED POSITION OF THE STRATA. 



The chalk and overlying formations seen in the cliffs be- 

 tween Hasborough and Weybourne may have been brought 

 into their present contorted and dislocated position by three 

 distinct kinds of mechanical movement; first, by ordinary 

 upheaval and subsidence, to which geologists are accustomed 



