348 



NATURAL SCIENCE. 



JULY, 



in the district, started to row down the Bure, hoping to reach 

 Wroxham Broad in time to enjoy, in the quiet of its reeds and rushes, 

 a sunset of which the clouded glory was worthy of Constable's 

 country. The Broad was less than a mile distant by land, but for 

 far more than that length the river kept at its uniform canal-like 

 width, without any sign of its intention of broadening out to satisfy 

 the definition : it was obvious that something was wrong, and the 

 quest was abandoned. Next day, from the deck of a wherry, the 

 matter was explained. Instead of the river passing through the 

 Broads, it kept sullenly aloof from them ; as we sailed down the river 

 there was Broad to right of us. Broad to left of us. Broad in front of 

 us, but by a series of ingenious twists and turns it managed to wind 

 through the whole lot of them, either eluding any direct contact with 

 them, or communicating only by a few narrow and often overgrown 

 passages (see Fig. 2). With some exceptions it is the same elsewhere: 

 the Broads are usually completely isolated from the rivers, which 

 may flow round three sides of them, as, e.g., at Surlingham (Fig. i). 



Fig. I. — Surlingham Broad and its relations to the Yare. (i inch to the mile.) 



Etymology, in fact, was, in these cases, as misleading as usual, and 

 was responsible for the very one explanation that was manifestly 

 hopeless. The orthodox definition having thus collapsed, one was 

 led to look around for some more reliable theory. 



Lakes are usually classified^ into six groups : (i) those occurring 

 in rock basins, eroded by glaciers or formed by other agencies ; (2) 

 those due to the elevation of parts of the sea floor ; (3) those lying 

 along the depressions formed by the folding of rocks ; (4) those due 

 to the damming up of a valley by moraines or landslips ; (5) those in 

 extinct volcanic craters ; and (6) those occupying mere hollows in 

 clay. The Norfolk Broads are but slightly above, or are even below, 

 the level of the sea, and are not separated from it by any rock rim, so 

 they do not belong to either of the first two classes- : the valleys in 

 which they lie are due to erosion through fairly horizontal strata, so 



1 See, e.g.. H. G. Seeley. Phillips' "Manual of Geology," ed. 2, 1885, pp. 134-7- 



2 A glacial origin has, however, been applied to the Broads (J. E. Taylor, the 

 Norfolk Broads and Jtleres, Geologically Considered. Trans. Nor/, and Nortuich Nat. 

 Soc, vol. i., 1872, pp. 30-40), but the little evidence advanced in support of this 

 conclusion is easily explained in other ways, and the direct evidence on the 

 contrary is overwhelming. 



