﻿212 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 9, 



" bone-bed " being the thickest and most widely distributed. The 

 following well-known examples will point this out : — 



Bone-bed at the base of the Lower Greensand at its junction 



with the Wealden. 

 Bone-bed at the base of the Inferior Oolite at its junction with 

 the Lias. 



Bone-bed at the base of the Lias at its junction with the New 

 Red Marl. 



Bone-bed at the base of the Mountain Limestone at its junction 



with the Old Red Sandstone. 

 Bone-bed at the base of the Old Red Sandstone at its junction 

 with the Ludlow Rock*. 

 If the Lias bone-bed be correctly assigned to the Trias, it would 

 then mark the commencement of the New Red Sandstone epoch, 

 instead of the close of the Liassic. 



I am indebted to my friend Mr. Lycett for some useful informa- 

 tion respecting the Lower Division of the Inferior Oolite in his own 

 district, and with which indeed he is in all respects so well acquainted. 



2. On some Points of the Physical Geography of North Ame- 

 rica in connection tvitk its Geological Structure. By Sir 

 John Richardson, M.D., F.R.S. 



[Communicated by Sir C. Lyell, F.G.S.] 



In the following brief communication it is my purpose to draw the 

 attention of the Society to the remarkable connexion that exists be- 

 tween the river- and lake-basins of North America and the geological 

 structure of that region. 



An inspection of Arrowsmith's or any other good general map of 

 the continent will show, that to the east of the Rocky Mountain chain 

 the chains of great lakes or the river-valleys have either a parallelism 

 to the Rocky Mountains, or run nearly at right angles thereto. 

 North of the St. Lawrence basin all the greater excavations lie in a 

 line parallel to the axis of the Rocky Mountains, and at the junction 

 of Silurian strata with a granitic formation, while narrower valleys, 

 occupied by the greater rivers, cross them nearly at right angles. 

 A few explanatory observations will make this more clear. 



The Rocky Mountain chain has a general course for 2500 miles, 

 or from the 30th parallel of latitude to the Arctic Sea, of North 26° 

 West ; that is, of about North-west by North. Its peaks rise from 

 1 2,000 to 15,000 feet above the sea, but passes occur at various places 

 at elevations of from 6000 to 8000 feet. The higher parts of the 

 range rise abruptly, but along the eastern base of the chain there 

 exists a belt, composed chiefly of sandstone, 150 miles wide, which 

 has a mean inclination of thirty-six feet in the mile, in its descent 

 from 8000 feet to 2500. From this belt to the shores of the 

 Atlantic, a distance of about 1800 geographical miles, the descent 



* See Sil. System, pp. 198-200. 



