276 Correspondence, 



In the gravel beds there are sometimes found fragments of rock, 

 with their edges mibroken, as if they had been brought down by 

 floating ice ; and there are other evidences which show that these 

 frozen masses must have exerted considerable influence in the foim- 

 ation of the level terraces. 



The bottom of the valley is occupied by a bed, which Sir Charles 

 Lyell characterizes as peat, and describes as being from ten to thirty 

 feet in thickness. 



Sir Charles Lyell speaks of this peat as having grown on the spot 

 where it is found, and as having required an immensely extended 

 period for its production. 



Mr. Prest\vich, in his paper read before the Eoyal Society in 1864, 

 does not speak of peat at all, but calls this bed " alluvium." 



Query First. — What is the nature and origin of the hed which oc- 

 cupies the bottom of the valley ? 



In England, and more particularly in Scotland, we find extensive 

 accumulations of peat. In some instances, the peat remains in its 

 natural locality. In such cases, the roots and stems of those plants 

 that grow in marshy soil, and by their decay produce peat, are 

 mingled through the whole mass, being of course more abundant in 

 the upper part, which has in consequence a soft and spongy con- 

 sistence. In other cases the more completely transformed particles 

 of peat, after having been saturated with water, have run down into 

 the hollows, leaving the undecomposed portion of the plants behind. 

 This variety of peat, when condensed and dried, is very tough and 

 hard, and is almost as heavy as coal. 



If the peat in the valley of the Somme has grown in the place 

 which it now occupies, we may expect to find a bed of, comparatively 

 speaking, rmiform thickness, having but little foreign admixture, the 

 whole mass being intermingled with the remains of the plants that 

 produced it, and these remains retaining the position they occupied 

 when alive. If it is an alluvium, brought down from the higher 

 grounds, we may expect to find beds of solid peat, with very little 

 trace of the plants that produced it, mingled with deposits of sand 

 and mud, and pieces of peaty soil, with vegetable remains lying in 

 various directions. If, as is most likely, some of the peat has grown 

 on the spot, and some has been brought down by the river, we shall 

 find the soil on the banks of the Somme of a very heterogeneous 

 description, containing peat of different kinds, intermixed with mud, 

 and sand, and clay. 



A more accurate examination of the bed which fills the bottom of 

 the valley seems to be required before we can determine its nature, 

 or its origin, or the time taken to produce it. 



Query Second. — Are the terraces on the sides of the valley of the 

 Somme to he ascribed to the effect of river-currents or to the action of 

 the seaf 



Along the coasts of Scotland we find in many places level terraces 

 of recent origin, from ten to fifteen feet above high-watur-mark. 

 They are formed of the sand and shingle carried up by the advancing 

 billow, and left behind in those places where the debris thrown up 



