24 0. B. B0GGILD. BOTTOM DEPOSITS. [norw. POL. EXP. 



elude even very coarse, stony components, such as, for instance, diluvial gravel 

 and the "Till" contain. With regard to the finest particles of less than O'Ol 

 mm., it will here also be immediately evident that there is a very essential 

 advantage in their curve being extended over a greater space, as a consider- 

 able percentage of them is usually found in the samples. It also becomes 

 possible to give the differences in the size of the grains in the clay, that can 

 be observed under the microscope, by making the highest point of the curve 

 correspond to the size of grain found in the greatest quantity. But this 

 part of the curve cannot, of coarse, be very accurate in detail, while the area 

 enclosed by the curve must naturally give accurately, the value found for the 

 percentages of the particles under - 01 mm. The only difficulty which cannot 

 in any way be surmounted in this mode of representation, is the impossibility 

 of determining how far to the left the curve is to extend, as there is no means 

 of finding out the size of the smallest clay-particles. That the sizes of the 

 particles do not decrease to an unlimited extent may be inferred from the fact 

 that all the clay does at last sink to the bottom in water, even though in 

 certain cases it may take weeks to do so. In none of the samples is the clay 

 of such fineness that 99 % of it will not have sunk to the bottom in the 

 course of 24 hours in a glass that is 20 cm. in height. I have always put 

 the lower limit at a size of about Vsooo mm. If it were in reality to be 

 a few units farther to the left, that part of the curve lying to the left of 

 001 mm. would be somewhat flatter as the total area must remain the 

 same; but in other respects the figure would not be altered in any essential 

 degree. By adopting the same mode of procedure everywhere, it will be 

 possible to make every difference between the various samples stand out sharply 

 and distinctly. 



The reason for choosing geometrical progression for representing the sizes 

 of the grains, is not only that by its aid it is possible to represent quite other- 

 wise than with arithmetical progression, the mechanical composition of any 

 deposit whatever, and thus by the same system to delineate all kinds of rock, 

 from the finest clays to the coarsest gravel deposits; but it is also because 

 this mode of representation is quite in keeping with the natural forces that 

 operated in the formation of the rock. If we examine a tolerably uniformly 

 grained rock, such as stratified sand, we shall always find that when most of 

 the grains are, for instance, 1 mm. in size, the percentages of grains measur- 



