362 DISTRIBUTION AND SIZE OF ERRATICS. chap, xviii. 



point ; moreover, we must not exaggerate the regularity of 

 the trains, as their width is sometimes twice as great in one 

 place as in another; and No. 6 sends off a branch at^, which 

 joins No. 5. There are also stx-agglers, or large blocks, 

 here and there in the spaces between the two trains. As to 

 the distance to which any given block would be carried, that 

 must have depended on a variety of circumstances; such as 

 the strength of the current, the direction of the wind, the 

 weight of the block, or the quantity and draught of the ice 

 attached to it. The smaller fragments would, on the whole, 

 have the best chance of going farthest; because, in the first 

 l)lace, they were more numerous, and then, being lighter, they 

 required less ice to float them, and would not ground so 

 readil}' on shoals, or, if stranded, would be more easily started 

 a<>-ain on their travels. Man}" of the blocks, which at first 

 siirht seem to consist of single masses, are found, when ex- 

 amined, to be made up of two, three, or more pieces, divided 

 b}- natural joints. In case of a second removal by ice, one 

 or more portions would become detached and be drifted to 

 different points farther on. Whenever this happened, the 

 original size would be lessened, and the angularity of the 

 block previously worn by the breakers would be restored, 

 and this tendency to split may explain why some of the fav- 

 transported fragments remain very angular. 



These various considerations may also account for the fact 

 that the avei-age size of the blocks of all the seven trains 

 laid down on the plan, fig. 50, lessens sensibly in proportion 

 as we recede from the principal points of departure of par- 

 ticular kinds of erratics, yet not with any regularity, a huge 

 block now and then recurring when the rest of the train 

 consists of smaller ones. 



All geologists acquainted with the district now under con- 

 sideration are agreed that the mountain-ranges A, b, and c, as 

 well as the adjoining valleys, had assumed their actual form 



