a water elevator used to raise and lower boats

• canal

• lock

• glacier

a ditch dug across land to connect one waterway to another

• peak

• canal

• mass production

a very tall building

• ice age

• glacier

• skyscraper

the overthrow of a system of government

• constitution

• revolution

• lock

the plan of government for the United States

• democracy

• constitution

• canal

a way of making large quantities of the same product

• glacier

• skyscraper

• mass production

a form of government in which people vote for their laws and leaders

• democracy

• ice age

• peak

the top of a mountain

• lock

• canal

• peak

when the earth entered a long cold period

• glacier

• ice age

• lock

a mile thick sheet of ice

• lock

• canal

• glacier