176 Profess&r H. D. Rogers, oh the Geology and [Feb. 8, 



their higher crests, and in less proportion, the older palaeozoic rocks 

 low upon their flanks. The Cascade chain, commencing in the huge 

 extinct volcano Mount Shaste, and crossing the Klamath, Columbia, 

 and Frazer rivers, dividing the northern desert from the Pacific 

 slope, is composed entirely of comparatively recent volcanic emis- 

 sions, though in some tracts it contains also belts of the older crys- 

 talline rocks. This mixed volcanic and plutonic character appears 

 to characterise this chain throughout its long course into Russian 

 America. 



F. The Pacific or Western Slope. 



Between the great Pacific chain and the western shore of the con- 

 tinent there extends the very long and comparatively narrow Pacific 

 slope, everywhere declining, more or less steeply, to the sea. Slender 

 in the Californian peninsula, it widens north of lat. 34^ to admit 

 the coast mountains and the gold-bearing valley of upper California, 

 here presenting three subordinate belts, covering a breadth of about 

 100 miles, which dimension it maintains to Vancouver's Island, and 

 beyond it. From the valley of the Sacramento, northward, its 

 surface becomes more rugged. 



The geological constitution of the Pacific slope is considerably 

 more diversified than that of the Atlantic slope, descending east- 

 ward from the Appalachians. It consists generally of tertiary strata, 

 mainly of miocene age : eocene, pliocene, and pleistocene, having 

 also been recognised. These tertiaries are generally undulated and 

 broken from violent crust movements, and in some quarters they 

 are extensively penetrated by eruptive volcanic rocks ; in other 

 tracts the older azoic and palaeozoic rocks, and still more ancient 

 gneissic strata, forming the spurs of the coast range, intrude them- 

 selves through the tertiaries, which have probably been deposited 

 around these ancient masses while they were above the waters. 



Gr. The Atlantic or Eastern Slope. 



This long and slender zone stretches from the Gulf of St. Law- 

 rence to the Gulf of Mexico, and descends with a gentle lateral 

 slope from the base of the Appalachians to the Atlantic coast. Its 

 several subordinate belts difi'er both in physical features and geolo- 

 gical structure. One sub-division, ranging from the Gulf of St. 

 Lawrence to the Hudson, through New Brunswick and New Eng- 

 land, has a hilly surface, and many rivers, which meet the tidal 

 level far inland from the sea. It contains short chains of rounded 

 hills, some of them mountains in size, and it is spotted with a 

 multitude of clear lakes and ponds, and is throughout admirably 

 watered. This region forms one general slope to the sea, not being 

 fringed on its ocean border, as the corresponding zone further south 

 is, by a true tide-water tertiary plain. 



In its geological composition, this north-eastern division of the 

 Atlantic slope consists generally of the older crystalline rocks, with 



