94 REPORT—1850. 
instance had he ever found the boulder clay, if not, as in the case of our common 
brick clays, a re-formation, dissociated from the scratchings and polishings. Every 
rock on which the clay rests in situ, if of a quality capable of bearing these mark- 
ings, is seen when newly uncovered to bear them. The more impressible pebbles 
and boulders, too, from top to bottom of the deposit, are similarly lined and polished ; 
and both rock and pebbles, when first laid bare, are as sharp and well-defined in their 
grooves and lines, even to the slightest scratch, as ifthe work of wearing them down 
had been performed but a day previous; though when subjected to the weathering 
influences, the exposure of a few months, or at most of a few years, serves to efface 
the marks. 
Now, from these data the inference seems unavoidable, first, that the rock on 
which the clay rests was scratched and polished either at the time when it was 
receiving its first coating of the clay, or so immediately before, that the markings 
were not in the slightest degree effaced when it was covered up; and, second, as 
the pebbles in the entire thickness of the deposit are also Scratched and polished, that 
it was not before, but at the time ; seeing that the process of scratching and polishing 
went on during the entire period of the formation, beginning with its lower layers, 
and not terminating until its uppermost were cast down. The dressed surfaces and 
the boulder clay are contemporary phenomena. Further, it is a significant circum- 
stance that small pebbles of only a few ounces are scarce less distinctly marked than 
the larger stones; it is further not less significant, and bears apparently in the same line, 
that in the preponderating majority of cases, at least, the smaller and flatter stones 
are marked in the lines of their longer axes. 
The agent which produced such effects could not have been simply water, whether 
impelled by currents or by waves. No force of water could have scarred with such 
distinct, well-marked lines, such small stones. The blacksmith, let him use what 
strength of arm he may, cannot bring his file to bear upon a minute pin or nail, until 
he has first locked it fast in his vice, and then, though not before, his tool bears 
upon it, and scratches it as deeply as if it were a beam of iron of a ton weight. The 
smaller stones must have been fastened ere they could have been scratched. Even, 
however, if the force of water could have scratched and furrowed them, it would not 
have scratched and furrowed them longitudinally, but across. Stones, when carried 
down a stream, or propelled upwards on a beach by the waves, present always their 
broader and longer surfaces to the moving force; and the broader and longer these 
surfaces are, the further are the stones propelled. They are not /aunched forwards, as 
a sailor would say, end-on, but tumbled forwards broadside. They come rolling down 
a river in flood, or upwards on the shore in a time of tempest, as a hogshead rolls 
down a declivity. In the boulder clay, on the contrary, most of the pebbles that 
bear marks of their transport at all were not rolled but slidden forward in the line of 
their longer axes. They were launched, as ships are launched in the line of least 
resistance, or as an arrow or javelin is sent in its course through the air. Mere 
water could not,have been the agent here; nor yet an eruption of mud propelled 
along the surface by some wave of translation produced by the sudden upheaval of 
the bottom or shore of the sea. 
When a large raft of wood, floated down a river, grates heavily over some shallow 
bank of gravel and pebbles resting on the rock beneath, it communicates motion, not 
of the rolling, but of the launching character, to the flatter stones with which it comes 
in contact. It slides ponderously over them, and they, with a speed diminished in 
ratio from that of the moving power, in proportion to the degree of friction below or 
around, slide over the stones or rock immediately beneath. And thus, to borrow the 
terminology of our Scotch law courts, they are converted at once into scratchers 
and seratchees. They are scratched by the grating raft, which of course moves quicker 
than they move; and they scratch in turn the solid mass or imbedded fragments 
along which they are launched. A vast number of rafts dropping down some river 
from day to day and year to year, and always grating along the same ledges of sand- 
stone, trap or shale, would at length very considerably wear them down; even the 
continual tread of human feet in a crowded thoroughfare soon wears down the trap 
or sandstone pavement and converts the solid stone into an impalpable mud ; and the 
materials of the waste, more or less argillaceous according to the quality of the rock, 
would be deposited by the current in the pools and gentler reaches of the stream. 
