GEOLOGICAL SEASONS. 177 



which so agreeably diversify the general surface of the 

 northern states are records of the last geologic winter, and 

 of the spring-time which followed. The rounded bosses of 

 the rocky outcrops; the grooved, striated and polished rock- 

 surfaces which everywhere underlie the soil and subsoil; 

 the deep-cut gorges of some of the rivers, and the broad ero- 

 sions of certain lake-basins, these and other familiar phe- 

 nomena find their explanation in the activities of a secular 

 winter, which clothed the northern hemisphere as far as 

 the latitude of 36 with a mantle of ice and snow. This 

 ice-period is one of the recognized epochs of geologic 

 history. 



Some of the most salient phenomena attributed to the 

 reign of glacier ice are smoothed and striated rock-surfaces, 

 and accumulations of rounded pebbles. Precisely these 

 phenomena have been detected among the rocks of remoter 

 ages of the world's history. More than thirty years ago, 

 the New York freolos^ists called attention to the smoothed 

 surfaces of the Medina Sandstone in the western part of 

 that State. They did not then dare to utter the conjecture 

 that these are glaciated surfaces; though recent opinion 

 strongly inclines in that direction. Foreign geologists 

 have made similar observations in numerous other forma- 

 tions.* In the Miocene System, that vast Swiss formation 



* Besides the cases cited in the text, we may mention tlie Cambrian or Lau- 

 RENTiAN (James Thomson, British Association, 1870, 88; A. C. Ramsay, Sivati- 

 aea Address^ 1880; Nature, xxii. 388; A. Geikie, Nature^ xxii, 402, in northwest 

 part of Scotland); LowEH Silurian (J. Carriclc Jloore, Quar. Jour. Geol. 

 Soc, Lond., V, 10; Philosopk. Mag., April 1865, 289; Geikie, Great Ice Age, 

 512; iivike'^. Manual of Geol., Ail \ Haughton m'Slc^C\m\.o(i\i's, Narrative of Arc- 

 tic Discoveries; Quar. Jour. Geol. Soc, xi, 510; A. C. Ramsay, -S/mnsm Address.^ 

 1880^; Upper Silurian, in Colorado (C. D. Walcott, Anier. Jour. ScL, III, xx, 

 222, 225); Devonian (A. C. Ramsay, Header, 12 Aug. 1865; Cumming, History 

 of Isle of Man, 86; Sclwyn, Phys Geog. and Geol. of Victoria, 1866. 15, 16; Tay- 

 lor and Etheridge, Geol. Surv. Victoria, Quarter-Sheet 13, NE; J. P. Lesley, 2d 

 Geol. Surv. Pa., i, 86, Portage Group; C. D. Walcott, A7ner. Jour. Sci., lU, xx, 

 13 



