OF NORTH AMERICA. 
69 
Modern formation. — The Modern deposits in North America are very extensive. The whole 
peninsula forming the southern part of Florida, is built by coral zoophytes, which continue to live 
and form the coral reefs of Florida. Agassiz, whose celebrity now belongs to both hemispheres, 
was the first to make known the actual formation of Florida. He has pointed out, step by step, 
the progress of the coral for the last century, and shown how these active and innumerable Ocean 
Laborers construct their works, and create the numerous islands known by the name of Key and 
Mangrove islands , and the Everglades of the Main land. 
The Mississippi river , below its junction with the Ohio , deposits at the time of the annual 
overflow all along its shore, great quantities of mud and all sorts of debris; at the mouth is formed 
an immense delta, which advances every year into the gulf of Mexico; and the actual shores of 
this gulf, from Lake Ponchartrain to the mouth of the Rio Grande, owe their origin to the allu- 
vium of the rivers which pour themselves into it. The Colorado of California also forms a delta 
near its mouth. In the Californian desert there are sand-dunes, that in the region of the Mohavee 
river rise nearly to the summit of mountains from five to six thousand feet above the level of 
the sea. 
Eruptive and Metamorphic rocks. The crystallized, metarnorphic, and volcanic rocks occupy at 
least a third part of the United States and the British Provinces of North America. They gener- 
ally form the mountainous parts of the country, and almost always make the contours of the hydro- 
graphic basins. I have divided these rocks into three groups, distinguished on the geological map 
by three colors. The first group includes the granite, sienite, gneiss, mica-schist, slate, etc. 
These rocks form the whole southern coast of Labrador, the Lawrentine mountains, the north- 
ern coast of Lake Huron, and the greater part of the northern shore of Lake Superior; they con- 
tinue through Rainy Lake, Lake of the Woods, and Lake Winipeg, to Coppermine river in the 
Polar region. The granitic rocks form more than the eastern half of Newfoundland , and also the 
eastern part of Nova Scotia. Notre Dame mountains, in the district of Gaspe, are an isolated cry- 
stalline mass , and there are several others further south , in the province of New Brunswick and 
the State of Maine. A broad band of crystalline and metamorphic rocks begins at the northern part of 
New York, the river Chaudiere near Quebec, and at Bangor in Maine, and embraces nearly all 
the New England States, a part of New York, New Jersey, Maryland, Pennsylvania, Virginia, 
the two Caroliiias, Georgia, and Alabama. This band includes the Green and White mountains, 
the Berkshire mountains, and the Blue Ridge of the Alleghanies. The crystalline rocks occupy a vast ex- 
tent of the country south of Lake Superior, extending toward the Upper Mississippi. West of the Mis- 
sissippi, there are five separated masses of crystalline rocks, all running from west to east. The 
most northern one is near the town of S‘ Louis , Missouri ; another is at Little Rock , Arkansas ; 
the third is between Fort Washita and the country of the Choctaw Indians; the fourth is marked 
on the map as the Witchita mountains; and finally the fifth is north of Fredericksburg, Texas. 
In the Rocky mountains, the Sierra de Yeinez, and the Sierra Madre, the crystalline rocks 
occupy narrow bands , fourteen or fifteen miles in width , and interrupted from time to time by the 
strata of Sedimentary rocks that cover them. In the Sierra de Mogoyon they are more extended, 
and are connected with those forming the immense Californian desert, the Great Basin, the Sierra 
Nevada proper, the Shasty mountains, the Coast Range, and the Cascade chain. More than Wo 
thirds of the Pacific region is formed of granite, sienite, and porphyry. 
