17 
and the curious markings found upon them. Sufficient reference 
has already been made to the first; the deposits occur in any or 
every district, and they rest ‘‘ unconformably’”’ as geologists say, 
upon everything below ; they fill up hollows, they lie at the foot of 
the hills, they are piled up at the mouth of valleys, or spread widely 
over the plains. As to their composition, sometimes they are of 
“‘sharp gravelly sand,” at others ‘‘ expanses of pebbly shingle, and 
more generally perhaps, of variously coloured clays.’ In the central 
counties of England we find ‘‘ sheets of clay embedded in an open 
gravely drift, composed of fragments of all the older rocks up to the 
chalk, masses of which, thousand of tons in weight are embedded 
in it. In other districts, as the middle counties of Scotland, large 
areas are covered with a thick, dark, tenacious clay, locally known 
by the name of “Till,” and enclosing rounded and waterworn 
boulders as well as angular fragments of all the older and harder rocks 
—granite, gneiss, greenstone, basalt, limestone. and the more com- 
pact sandstones. Let me call your attention especially to the 
presence of such miscellaneous collections in one locality. One is 
never surprised at the occurrence of blocks of stone of any size, or 
in any number, provided they are natives, t.e., so long as they 
belong to the district in which they are found. We naturally 
expect to see in our own neighbourhood blocks of the sandstone of 
which the cliffs and inland slopes are composed. Nor do the people 
of Cornwall feel astonished at the masses of granite scattered on 
their hills or embedded in the ground. But suppose that such 
blocks of Cornish granite lay strewn around Folkestone, and the 
Folkestone sandstone rocks were on the Cornish heights, 
then they would be foreigners, not natives, and their 
presence would require explanation, just as much as would the 
- presence of a colony of New Zealanders in some recess of the High- 
lands. Most striking among such blocks are solitary specimens 
found in Cumberland, Scotland, and Switzerland—composed of 
stone, different to any kind known for miles around, lying like 
solitary strangers in a strange land, or a stranded vessel on an un- 
known shore. “ Erratics” they are called—wanderers. At Pre- 
volta, in the Alps, there rests upon hills of limestone, along with 
thousands of others, the erratic shown on the screen, a block 50ft. 
long, 40ft. broad, and 25ft. high, with all its edges and angles perfect; 
it is composed of granite, and weighs about 5,600 tons. How came 
it there? Note again on the next slide the ‘perched blocks,” as 
they are called, seen by every tourist in the Pass of Llanberis. 
Almost everywhere on the Jura Mountains, Sir C. Lyell tells us, 
lie these granite, gneiss, and other crystalline blocks, which un- 
doubtedly came across one of the widest and deepest valleys in the 
world, from the Alps, which are fifty miles distant. How did they 
