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these wedges of limestone north-westward does not exceed fifty 
feet in a mile in any case that has yet been discovered, so that the 
gradient in the highest rate of thinning observed is only about 
1 in 105, a slope so gentle even in that extreme case as to be 
practically imperceptible. Now and then, during the slight pauses 
in the depression of the land, the deltas advancing from the north- 
west carried out thin sheets of sediment, which were spread out 
far and wide over the newly-formed limestone ; but in much less 
quantity towards the west than in the opposite direction. Then, 
as more rapid sinking ensued, and the shore line and its deltas 
were carried again far to the north-west, more thin wedges of lime- 
stone were formed. So sheet upon sheet, each a trifle thicker 
towards the south-east, and thinner in the opposite direction, were 
laid down, and the Mountain Limestone was formed. To the 
east of the Lake District it is true that the coarser nature of the 
sediment, and the larger percentage of deposits of mechanical 
origin to those of organic, shew that the delta in that area had 
early advanced farther towards the south than in the present area 
of the Lake District. But around what is now the Lake District, 
it is a very remarkable fact that the limestones accumulated during 
this period are singularly pure in themselves, and are also much 
less interbedded with sedimentary material, than are the beds of 
the same age only a few miles to the east. 
We have, then, to picture to ourselves the present Lake District 
as a submerged area, nearly flat in shape, and slowly becoming 
buried beneath a pile of wedges of pure limestone. What shoals 
and islands there were lay, not where the Lake District is now, 
but in the areas to the eas¢ of it; and what land there was lay to 
the north and north-west. So, if we study the beds forming the 
Mountain Limestone in Cumberland and Westmorland, we find 
those beds thickest towards the south and south-east, and thinnest 
towards the north and north-west. Hence, instead of being fully 
two thousand feet in thickness as it is in the southern part of the 
area, the Mountain Limestone on the northern side of the Lake 
District may, in places, not much exceed thirty or forty feet. So, 
also, in regard to the mechanical sediments deposited between the 
