J. LeConte—Formation of the Earth-surface. 453 
well known. If I deserve any credit in this connection, it is in 
giving something more of definiteness to the conception and espe- 
cially in showing its connection with the formation of the Appalach- 
wan chain. 
whole, this has probably been the case throughout the geologi- 
cal history of the earth, as has been so beautifully shown by 
a for the North American continent. The recent observa- 
ard the proc 
ines of thick sediments, rise of geo-isotherms and aqueo-igne- 
ous softening determine lines of yielding; then crushing to- 
gether horizontally and swelling up vertically forms the chain ; but 
once the yielding commences, then mechanical energy is changed 
into heat, which may thus be increased to any amount and pro- 
duce true igneous fusion. 
