Crosby.] 
120 
[May 21, 
behind when the finer material is removed by the carts ; and it is 
thus sometimes possible to observe in one compact group all the 
bowlders derived from a considerable and fairly definite volume of 
the till. Any one who gives attention to this matter for the first 
time will probably be surprised to find what a small proportion of 
the normal till the stones and bowlders really make. These hard 
obtrusive masses attract attention and thus usually count for much 
more than their real value. But it is doubtful if stones and bowl- 
ders more than two inches in diameter often form more than five to 
ten per cent, of the till, and the instances will certainly be very 
rare and local where they form more than twenty per cent. It thus 
becomes evident that the composition of the main part of the till 
may be fairly represented by comparatively small samples. The 
samples analyzed varied from about eight to sixteen pounds in 
weight, when first brought in. They were, in most cases, carefully 
dried for several da}^s at a temperature of about 100° Cent, losing 
variable proportions of water, according to the state of the weather 
when collected. No account was taken of this hygroscopic mois- 
ture, but the dry weight was obtained in advance, simply as a 
check upon the subsequent manipulation and weighings. The 
analyses were chiefly mechanical. Each dried sample was first 
thoroughly soaked in a sufficient but limited amount of water and 
all the large pebbles or stones careful ly washed out of it, and then 
submitted to a series of wet siftings, the product left on the sieve 
each time being well washed and care taken to save all the water 
used in this way. Six sieves in all were used, of the following 
sizes: 4, 6, 12, 20, 40 and 60 meshes to the linear inch; afford- 
ing six different grades of gravel and sand. The water, which 
now amounts to two or three gallons, is quickly decanted and a 
considerable volume of very fine sandy sediment obtained. This 
seventh residue is washed as before, and the water is now allowed 
to stand quietly for several minutes and then slowly decanted, af- 
fording an eighth residue, which is less abundant than the seventh 
and excessively fine, but still gritty when tested between the teeth. 
This is washed, and all the water, with the finer portions of the till 
still mixed with it, is then transferred to a deep vessel and allowed 
to stand quietly over night. The next morning the water, which 
although usually almost clear, is sometimes distinctly or strongly 
turbid, is drawn off quietly with a siphon, leaving a voluminous 
ninth product which I have called the siphon residue. It looks 
