112 THE LAKE-BASINS OF IARCONN AUGHT. 



course, there would be one or more small shallow lakes 

 on the site of the lagoon. That many of the bars 

 or ridges of gravel found in the valleys of larcon- 

 naught were once similar to the bar at Cleggan is 

 evident, as in addition to the bar, the old stream- 

 course or embouchure is still visible, also the terraces 

 formed at the margin of the water in the lagoon. The 

 accompanying map (PL III., fig. 17) represents 

 the site of one of these ancient lagoons, the gravel 

 banks being the remains of the ancient bar; there 

 are also terraces that not only show the limits of the 

 lagoon, but also the sea margin on both sides of the 

 valley outside the bar. 



In some bays or estuaries similar bars to that at 

 Cleggan cannot form for various reasons. First, the 

 stream may have greater power than the tide ; second, 

 the river may be subject to freshets, and during floods 

 all the sand that had accumulated will be swept away, 

 and spread more or less evenly on the bottom of the 

 bay ; and third, the stream may be so inconsiderable, 

 that it cannot form a back-water, between which and 

 the influx of the tide the bar would form. In the 

 latter case a semi-bar sometimes forms, the conditions 

 being unfavourable for its extension across the mouth 

 of the stream, and such a bar occurs as a gravel bank 

 at the village of Leenaun, Killary Harbour. 



It may be said that the streams at present flowing 

 into the lagoon at Cleggan are too small to have 



