388 W. 8. Bayley — Spotted Rocks from Minnesota. 



declivity, and every change in declivity means modification in 

 competence and variation in deposits. So fluvial deposits are 

 heterogeneous. Moreover rivers take the paths of least resist- 

 ance and flow freely in deep channels, and in selecting their 

 courses they avoid the higher levels and seek depressions 

 which they continually deepen ; the deeper the initial depres- 

 sion the more rapidly is it deepened ; and thus fluvial action 

 ever accentuates irregularity of surface. So fluvial plains are 

 multiform. But the forces concerned in the formation of the 

 Middle Atlantic slope terraces acted horizontally over great 

 distances and with uniform energy for a considerable period, 

 filling depressions, softening contours, and obliterating 'relief, 

 yet so gently that essential homogeneity of deposit in the hori- 

 zontal direction and essential uniformity in surface prevails for 

 miles. Only the undulatory and horizontally acting force of 

 waves appears competent to produce so great expanses of uni- 

 form surface and constant structure as are exhibited in this 

 region 



By the testimony of terraces and shore-lines the existence of 

 inland seas and lakes of Quaternary age in many portions of 

 the world has been proved to the satisfaction of geologists ; 

 yet although the middle Atlantic slope terraces have been more 

 deeply graven by erosion and reduced by weathering, they are 

 more extensive than those of any of the extinct or shrunken 

 Quaternary lakes in the country ; and their testimony is equally 

 decisive. 



[To be continued.] 



Art. XXXII. — On some peculiarly spotted Rocks from Pigeon 

 Point, Minnesota ; by W. S. Bayley. 



[Published by permission of the Director of the IT. S. Geological Survey.] 



The northeastern extremity of Minnesota is known on the 

 charts as Pigeon Point.* This point extends in an easterly 

 direction into Lake Superior. It is separated from Canada by 

 the waters of Pigeon Bay and Pigeon Piver. Its length is 

 about three and a half miles. Its width varies from a few 

 hundred feet to a little less than half a mile. The greater por- 

 tion of its mass consists of a great dyke of coarse olivine gab- 

 brof or diabase. Associated with this is a large quantity of 



* The exact location of the point is T. 64 N\, R. 7 E. of the 4th principal meridian, 

 Sections 25, 26, 27, 28, 29, 30, 31 and 32. 



f Of. Irving : Copper-Bearing Rocks of Lake Superior, Monograph V, U. S. G-. 

 S. Washington, 1883, p. 369 et seq. 



