BOULDERS 39 
can we say but that we have found the rocks where 
the granite and slate boulders came from, and that 
they must have been carried to the plain by a glacier ? 
Have we not traced the direction of the ice-flow as 
indicated by the scratchings, and when we compare 
the boulders with the mother-rocks are they not 
similar in texture and composition ? 
Why, boys and girls, you say Sherlock Holmes 
was a wonderful detective, and when you read about 
his doings, which are pure fiction, you think you 
would like to do some detective work on your own 
accounts. Surely you can be detectives in the very 
best sense of the word. Have I not just shown you 
how to solve a problem of Nature? If you devote 
yourselves to Nature-study you will find some almost 
brain-cracking problems to solve, and you will be 
able to turn your intelligence to better account than 
in solving criminal mysteries, fictitious or real. You 
will find some rock fragments that have been carried 
by glaciers which have not been scratched, ground, 
or rounded. Such fragments have been carried on 
the top of the ice-sheet, and have not been subjected 
to rough usage. They have, of course, dropped to 
the ground when the ice melted. A glacier, it should 
be noted, does not travel as a solid block of ice, but 
more after the manner of slightly melted pitch, yet 
much slower. Glaciers are also credited with laying 
down the Boulder-clay—a clay which is, full of 
boulders of various kinds of stone. 
This chapter has grown longer than I intended it 
to be ; yet how little I have told, and how much there 
is to tell! I have written little or nothing about 
fossils, which in truth demand a volume to them- 
