NIAGARA FALLS AND VICINITY 



41 



of the cuesta, and ultimately prolonged these gullies into gorges, 

 and carried the drainage into the subsequent streams. Streams of 

 this type, which have their representatives in all coastal plain 

 regions, have been called ohscqucnt streams,^ their direction of flow 

 being opposite to that of the consequent streams. The following 

 diagram (fig. 4) illustrates this type of a stream and its relation to the 

 subsequent and consequent streams. To this type of stream belongs 

 the ancient St Davids gorge, as will be shown more fully in subse- 

 quent pages. 



Fig. 4 Diagram of a portion of a dissected coastal plain, showing old-land on the left, and two 

 cuestas with their accompanying inner lowlands. Three consequent streams have breached the 

 cuestas, and subsequent streams from the lowlands join them. An obsequent stream is shown in 

 the center of the outer cuesta. 



If we assume that during the greater part of the Mesozoic era, 

 the land in this region remained in a constant relation to the sea- 

 level, it becomes apparent that the southward retreating infaces of 

 the cuestas formed by the resistant members of the Paleozoic rocks, 

 became lower and lower, as the southward inclination of the strata 

 carried the resistant beds nearer and nearer to sealevel. Eventually 

 the escarpment character of the infaces must have become obsolete, 

 from the disappearance, beneath the erosion level, of the weaker 

 lower strata, which permitted the undermining of the capping beds. 

 When this occurred, the capping strata alone contin,ued ex- 

 posed to the action of the atmosphere, and, from a cliff char- 

 acter, their exposed ends were planed off to a wedge shape, thin- 



nV. M. Davis 



