the elementary form': of bulling*, and post Columbian chronicles 
give us glimpses of the higher development that came under the 
observation of the Spanish conquerors, but arched ogle remains 
supplement the lessons of the historic period* he find construe* 
tions of great variety and of remarkable preservation in the 
Mississippi Valley, in the pueblo country, on the Mexican 
plateau, in Yucatan, Guatemala, Honduras, end in South America* 
By the aid of these we see how the midden and the earth mound 
develop into the pyramid with its multiple stairways of cut 
stone; how the walls change from irregularly placed stone and 
clay covered wicker to massive structures of accurately hewn stone 
how the chamber spaces, ceiled at first with went timbers sub- 
ject to quick decay are spanned later by the offset arch of 
stone* ue see supported on this native arch the concrete roof 
so massive to defy the earthquake and support the forests of 
successive centuries; we see the multiplication cf stories, 
tier on tier; we see the spanned space limited at first to a 
few feet, increase indefinitely to the many vaulted roof support- 
