Gregory — Progress in Interpretation of Land Forms. 113 



half-century has been regained and how rapid the 

 advance in the knowledge of land sculpture since the 

 canyons of the Colorado Plateau were interpreted. 



Features Resulting from Glaciation. 

 The Problem Stated. 



Early in the 19th century when speculation regarding 

 the interior of the earth gave place in part to observations 

 of the surface of the earth, geologists were confronted 

 with perhaps the most difficult problem in the history of 

 the science. As stated by the editor of the Journal 

 in 1821 : 30 



' ' The almost universal existence of rolled pebbles, and boulders 

 of rock, not only on the margin of the oceans, seas, lakes, and 

 rivers ; but their existence, often in enormous quantities, in 

 situations quite removed from large waters ; inland, — in high 

 banks, imbedded in strata, or scattered, occasionally, in pro- 

 fusion, on the face of almost every region, and sometimes on the 

 tops and declivities of mountains, as well as in the vallies 

 between them; their entire difference, in many cases, from the 

 rocks in the country where they lie — rounded masses and peb- 

 bles of primitive rocks being deposited in secondary and alluvial 

 regions, and vice versa; these and a multitude of similar facts 

 have ever struck us as being among the most interesting of 

 geological occurrences, and as being very inadequately accounted 

 for by existing theories." 



The phenomena demanding explanation — jumbled 

 masses of "diluvium,'' polished and striated rock, 

 bowlders distributed with apparent disregard of topog- 

 raphy — were indeed startling. Even Lyell, the great 

 exponent of uniformitarianism, appears to have lost faith 

 in his theories when confronted with facts for which 

 known causes seemed inadequate. The interest aroused 

 is attested by 31 titles in the Journal during its first two 

 decades, articles which include speculations unsupported 

 by logic or fact, field observation unaccompanied by 

 explanation, field observation with fantastic explanation, 

 ex-cathedra 'pronouncements by prominent men, sound 

 reasoning from insufficient data, and unclouded recogni- 

 tion of cause and effect by both obscure and prominent 

 men. With little knowledge of glaciers, areal geology, 

 or of structure and composition of drift, all known forces 

 were called in: normal weathering, catastrophic floods, 



