CXIiv PROCEEDINGS-PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
the cist is formed are very massive and heavy, and it seems to me 
extremely likely that its builders would go down to the solid rock to 
get a firm foundation for it. If that is so, and if archaeologists can 
determine for us the age of the cist, then we can tell pretty accurately 
how long it has taken for ten inches of solid sandstone, undisturbed 
by any surface action, to break up into a layer of “brash” of corres¬ 
ponding thickness. From the base of the cist to the surface soil, 
a space of about six feet, the brash gradually merges into a dark- 
coloured sandy loam. 
4. The fourth and last section which I shall take is one in the 
alluvial district of the Carse of Gowrie. At Mugdrum Island, some 
three years ago, a deep boring was made by Mr. Alex. Davidson, 
preparatory to sinking a well, and a record of the beds passed 
through was kindly kept and given to me by the late Mr. John 
Young, C.E. These are shown in the following table :— 
1. Sandy Clay, .... 
2. Muddy Sand, 
3. Gravel, ..... 
4. Fine Brown Clay, .... 
5. Fire Clay, - - - - 
6. Muddy Sand, .... 
7. Sandy Clay, with Stones, 
8. Clay, with Stones, 
9. Bound Sand, with Stones, 
10. Bound Sand, .... 
11. Broken Sandstone, - - - 
12. Red Fire Clay, .... 
13. Flard Sandstone, interstratified with Fire Clay, 
0 
J 
feet 
9 
inches, 
9 
55 
6 
55 
2 
5 5 
4 
5 5 
35 
5 5 
0 
5 5 
7 
55 
4 
5 5 
11 
5 5 
0 
5 5 
19 
5 5 
4 
5 5 
5 
5 5 
0 
5 5 
2 
5 5 
0 
5 5 
I 
5 5 
0 
5 5 
9 
5 5 
0 
5 5 
2 
5 5 
6 
5 5 
indefinite. 
Total thickness of Soft Strata, - 107 feet 9 inches. 
It will be seen at once that we have here a soil very different 
from those we have previously been examining, both in regard to its 
composition and its great thickness. The beds from No. 1 down to 
No. 9 represent material not decomposed on the spot, but brought 
from a distance, and deposited during several successive periods. 
Indeed, if we come to examine its history more particularly, we shall 
find that this material represents the waste of rocks over a very wide 
and diversified area, covering the whole of the region drained by the 
Tay and its tributaries, and extending even far beyond that, if we 
include the ice-transported material. On the principle, therefore, 
that diversity of composition makes a fruitful soil, we are prepared to 
find that the lands of the Carse of Gowrie give a good return to the 
agriculturist, and especially to the fruit grower, after their mechanical 
disadvantages have been overcome by cultivation. 
Passing from these four local examples, let us now enquire 
generally what soil is, and how it has been formed. To the average 
agriculturist,—or, indeed, to the average man or woman,—soil, or 
earth, is simply the medium in which plants grow, and from which 
they obtain a portion of their nourishment. This soil, they will tell 
you, if they have thought of the matter at all, has always covered the 
face of the land, or, if it has changed at all, it has been through the 
decay of the plants which grew on its surface, producing so-called 
vegetable mould. Geology, however, has a different story to tell us. 
