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



scale; 005 lies between -^ and ^, and by calculation, its distance from ^ 

 is found to be 032 of a unit; 01 lies between ^ and j^, and is found to 

 be at a distance of 0"64 of a unit from -fa. Among the parts into which the whole 

 sample is divided by washing, the particles measuring 1 — 2 mm. and 05 — 1 mm. 

 each occupy 1 unit, those measuring 005— 0"5 mm. 3'32 units, and those mea- 

 suring 01 — 0"05 mm. 2"32 units, while the finest particles, of less than - 01 mm., 

 extend over a number of units, which cannot be exactly determined. When 

 stVt is placed, as already stated, as the extreme limit of the scale to the left, 

 this gives 6'36 units for this part of the sample. If we now divide the per- 

 centages of the various sizes of particles found by washing, by these figures, 

 which give the number of units embraced by each size, we obtain the average 

 height attained by the curve in the space in question. By being content with 

 the horizontal lines only, we should have obtained a very poor representation 

 of the actual thing, where sudden leaps from one size to another are never 

 found. I have therefore always rounded off the curves, and two different 

 methods may be employed for getting at the correct form. The surest is of 

 course to examine the samples themselves under the microscope or with a 

 lens. If we place, for instance, a sample of the size 001 — 005 mm. under 

 the microscope, and examine the grains of these particular sizes, a fairly accurate 

 idea may be formed as to what are the intermediate sizes that are most abund- 

 antly represented in the sample, and thus as to where the highest point of 

 the curve will lie, and also to some extent how much higher it will be at this 

 spot than at other parts. A consideration of the adjacent sizes will also to a 

 great extent assist in the determination of the form of the curve. For in- 

 stance, it is evident that when we find a very small percentage of one size, 

 the curve for the size or sizes that lie next to it, falls down very rapidly to- 

 wards it. Both ways always lead to the same result. 



It will be seen that there are always two curves drawn. The upper one 

 gives the quantity of all the constituents of the sample, the lower the quantity 

 of the true mineral particles. Two areas are thus obtained, one for the clayey 

 matter, the other for the mineral particles, here designated, for the sake of 

 brevity, respectively clay and sand. This division is made by counting under 

 the microscope a number of particles, and calculating the percentage of clay 

 and sand in each separate size. This admits of being accomplished with 

 tolerable accuracy so far as the coarser particles are concerned; but in the very 



