440 THE CANADIAN NATURALIST. [Vol. vii. 



According to their relation to the neighboring eminences, and 

 to the straits and gorges between them, these (now elevated) 

 shoals take varying forms — forms of which there arc four prin- 

 cipal types, viz. — 1st. The Weather Shoal. This has been cast 

 down before a hill, or on one or both sides of the entrance to some 

 gorge : it has usually a rounded form sloping gently downward to 

 the plain in front, and often having a hollow behind it, separating 

 it from the solid rock of the hillside. Gravel knolls of this na- 

 ture may be seen at the falls of the Piskahegan River, Charlotte 

 county, and at the gorge leading from the valley in the 8. W. 

 corner of Sussex parish in Kings county to that of the Hammond 

 River. 



2d. The Let-Shoal. This has gathered behind hills or the 

 outlets from gorges. Ridges of this kind are quite numerous. 



3d. The Centre-Shoal. This is an accumulation of gravelly 

 materials formed in the open space beyond a gorge or upon the 

 top and slopes of rocky ridges, either covered with or partly 

 denuded of Boulder-clay. " Giant Gh-aves " and Whale-backs 

 are of this group: the former being for the most part gravel 

 throughout their whole depth, and comparatively small ; the 

 latter having usually a substratum of Boulder-clay. 



4th. Horseback, Boarsback or Escar. This type of gravel bank 

 usually extends along the top of rounded slate ridges, forming a 

 crest often many miles in length, or it forms a connecting bank 

 between neighboring rocky hills. These long and uniform ridges 

 appear to have been formed at the contact of two branches of 

 the polar current, moving side by side but with different velo- 

 cities, thus giving, especially in the shallower water at the top of 

 the ridge where their edges meet, the effect of an eddy. There 

 is an endless variety of intermediate forms connecting the four 

 types of gravel ridges, but they are all evidently due to the 

 varied action of the current, now stopped by an opposing hill, 

 and anon rushing swiftly through some gorge and scouring it 

 out to the rocky bottom ; or again, at a sudden bend of the val- 

 ley, rising out of it to course across the adjoining submerged 

 ridges. 



To show at a glance the most characteristic of the gravel- 

 ridges the following table — in which all the bearings are cor- 

 rected to the true meridian — is added. When two bearings are 

 given the first is that of the northern end of a ridge. One ridge 

 observed by Prof. L. W. Bailey is marked with an asterisk, and 

 those seen by Mr. R. W. Ells by an obelisk. 



