134 Peacock: Lincolnshire Naturalists at Torksey. 



beds of ligfit red clays, veins and blocks of gypsum, and thin 

 lines of ripple-marked sandstone occur throughout ; and it is 

 only when the highest beds of the Keuper Marls are reached that 

 any kind of stratification is discernible ; bands of red, blue, and 

 grey earths occurring just before the rocks dip under the Rhcetic 

 beds at Lea. ' 



As to the gypsum, quoting again from the same paper, 



* in the Lower Keupers at Retford, up to the Red Marls at 

 Gainsborough, this mineral is invariably fibrous, or satiny, in 

 character ; in the higher beds, however, it changes, at first to 

 rubbly patches, and, afterwards, to large, granular, or saccha- 

 roid blocks ' ; and this change, as Mr. W. Whitaker suggested 

 at the time, may possibly mark the division of the strata, and be 

 the only outward evidence of the passage from one bed into 

 another. 



The occurrence of a cliff in this neighbourhood is of sufficient 

 interest to attract attention. At Gainsborough the river has 

 carved out an escarpment in the Keuper on the east side of the 

 town, which, after sinking to nearly a level at Knaith, rises 

 again to form the well-wooded cliff at Gate Burton, and then, 

 after a long stretch of low-lying land — past Littleborough, 

 Marton, Torksey, and Laneham — it rises once more into the 

 picturesque cliff of Newton, which was the main geological 

 feature of this day's excursion. 



It is to the river that we are indebted for all we know about 

 the Keuper deposits in this district ; and there are other lessons 

 we may learn from it as well. Wherever river-valleys are wide, 

 and have a flat, level plane-surface, like the valley of the Trent 

 in this neighbourhood, the streams flowing through them are 

 sure to wind along in curves, and, the more they wind, the 

 wider the valley becomes. If the flow kept in a straight course 

 the shape of the valley would soon be narrowed and altered. 

 And the cause of this is obvious — wide, flat river-valleys being 

 due to the advanced age of the rivers that flow through them, 

 and their consequent loss of power. When rivers are young 

 and in their prime they rush straight through all opposing 

 obstacles, however hard, as the Trent did when it poured down, 

 from the heights of its sources on the west, on to the great 

 oolitic plateau, which then covered the land, far and wide, 

 round Lincoln, cutting it through, and leaving behind it the 



• Lincoln Gap, 1 with the wide denuded liassic area on the west; 

 and, aided by the Welland, the Nen, and the Ouse, the 4 great 

 bay of the Wash on the east.' But when rivers, through 



Naturalist, 



