]:V2 THK ICK ACK IN CANADA. 



incnm.siiii,' in sizo, and actually liccftiuos a niim'atuvo Ikt}^, 

 containing' sonic tlioitsands of cnl»i(^ feci of ice and iniid, 

 and still retainini' a hnovancv wliicli will cniddi! it, after 

 a tliaw, (hiring' lii,i,'li sprini;- tidi's, to break awjiy wiili a 

 load of (/''hri>i, and carry it eitlior out to sea (»r up the 

 estiuiry, and, if it should chance to he stranded aj^ain, it 

 will prohably leave a |)orti()n (»f its Imrden, jirovided it 

 has not melted oil' durinij- its vovau:e with the tide, lint 

 there can he no douht that S(tine of the attached sand, 

 mud, or shinj^le is melted oil' durin;^' the journey of the 

 block or miniature herfj, and drops into the hed of the 

 river or estuary. Fn reality, these ice-cakes, when in 

 motion, are per])etually strewing' tlu^ bottom with trans- 

 ported materiid and biin^inn- a portion from one place to 

 another, duriui,' about five houi's of the tlood, and ciirryin*^ 

 part of it l>ack ai^ain, duriiin' five hours of cblt, to the 

 limits of the backward and forward tidal ran<,'e of each 

 particular ice-cake. lUit when they accumulate in an 

 eddy, they become ])owerful carriers and dej)ositors of 

 detritus, and if artificial obstructions be introduced so as 

 to form an eddy in the usual course of the ice-stream, thi; 

 accumulation nmst necessarily be very rapid." 



6.— CONTINENTAL ELKVATION AND DEI'RKSSION. 



6. IJefoi'C leavint^ this summary of causes, it is necessary 

 to make a few ,t^eneral stater 'Mits res[)ectin_u; elevation 

 and depression. The first ano most important is that, 

 from the great I'liocene elevation onward, sul)sidence 

 and re-elevation were always in prot,ness. At each stage 

 of these there must have been corres])onding geogra- 

 phicfil conditions and varying facilities for distribution 

 of travelled detritus. In regard, therefore, to the causes 

 of any particular deposit, one of the most important 



