xv SE< i$ 



we construct a section across the London basin on 

 a true scale, or examine that which has been constructed 

 and pulihOir.i l.\ the Geological Survey on the scale of 

 hen to a mile, we learn that so flat is the basin, so 

 small tin- thickness of clay (500 feet) in proportion to the 

 breadth of country over wh spread (24 miles), 



that we need to look with some little care to be assured 



-.here is really any basin at all. 

 The next IHWU to be attended to in the construction 

 of a horizontal section is the choice of the line of ground 

 across which it is to lie drawn. It may be designed 

 either to show the general structure of the country or 

 the arrangement of the rocks in some particular pan of 

 it. In any case, while taking it over those portions of 

 the ground where the sir vs. turc is best seen, we should 

 always bear in mind that it must pass as nearly as 

 possible at a right angle to the strike of inclined strata. 



usly, a section coincident with the strike would 

 make highly inclined beds look horizontal. 



When the time arrives for a section to be drawn, 

 the first thing is to insert the outline of the ground. 

 The actually observed geological data, such as dips, 

 faults, and other facts, are then placed upon that outline. 

 If necessary, search is made on either side of the line of 

 section for additional materials to fill in the blanks in the 

 section. The lines found at the surface are then pro 

 longed downward, and the section is filled in. To make 

 these stages more clearly understood, let us suppose that 

 we are required to draw a section on a true scale (say of 



i hcs to a mile) across a piece of ground, v, 

 on some datum-line, the sea level, for instance, on which 



