July 27, 1917] 



SCIENCE 



91 



enduring for possibly many thousands of 

 years. 



In modern times, and in very recent geo- 

 logic times as well, there have been minor fluc- 

 tuations or pulsations in climate in various 

 parts of the earth, as ably demonstrated by 

 Briickner, Huntington and others. The 

 " Briickner cycle," about thirty-five years in 

 length, illustrates one type of pulsation. 

 Harm, Melldrum, Douglass, and others have 

 observed an eleven-year period to be about the 

 average leng-th of time between the maxima 

 of wet or dry conditions. While the length 

 of the cycles or periods may vary, the com- 

 binations of these shorter cycles of climatic 

 changes are considered as making up the 

 grand or climatic cycles, which are the ones 

 best known in geology. 



If the pulsatory theory of climatic change 

 is a true interpretation of the observed facts 

 of recent times, as seems very probable, then 

 one may naturally inquire if similar pulsa- 

 tions or minor changes in climate have not 

 occurred in the geologic past. If they have, 

 what evidence, if any, is to be found in the 

 rocks? The work of Barrell, Sayles, Case 

 and others, in their studies of sedimentation, 

 seems to definitely correlate climatic fluctua- 

 tions with various phases of erosion and 

 deposition. It may be of interest to submit 

 some facts which may prove to be additional 

 evidence of climatic pulsations, as afforded 

 by certain " sedimentary " rocks. 



The writer, in the course of a study of the 

 sandstone formations in the foothills south- 

 west of Fort Collins, in northern' Colorado, 

 came to the conclusion that much of this 

 sandstone is of subaerial, arid not subaqueous, 

 origin. The sandstones of this region are 

 commonly referred to as " Eed Beds." The 

 stratigraphic names are the Lyons, and the 

 Lykins formations. 



In the most prominent ridge of the Lykins 

 outcrop are located a number of quarries from 

 which flagging and building stone have been 

 taken for many years. One prominent 

 feature of much of this, stone is its variegated 

 laminations. These * are usually alternate 

 layers of white- and brpwn sands, although 



other colors are occasionally found. These 

 layers vary in thickness from about 0.5 mm. 

 to 30 or 40 mm. In a number of cases the 

 white layers are much thicker than the brown, 

 while in many other cases the two kinds of 

 layers are nearly equal in thickness. Also, 

 the brown layers are often thicker than the 

 white. Very thin alternate layers often 

 occur, and there are usually many of these in 

 a group when they do occur. 



Examination of the character of typical 

 samples from these layers shows, essentially, 

 the following facts : 



1. The white layers are composed almost 

 wholly of very well rounded grains of white 

 quartz, with scattered specks of iron oxide; 

 the quartz grains are nearly uniform in size, 

 the largest being rarely over 1 mm. in di- 

 ameter, and the smallest about 0.3 mm. in 

 diameter; the white layers are almost wholly 

 free of any colored cement, and of angular or 

 even subangular grains; many of the grains 

 are pitted; wind ripples are frequently found 

 at the top of a white layer, on exposed bedding 

 planes. 



2. The brown layers are composed almost 

 wholly of angxilar and subangiilar grains of 

 many different sizes, from very small to over 

 1 mm. in diameter ; comparatively few rounded 

 grains are present; the color is due to a coat- 

 ing of iron oxide on most of the grains. 



These differently colored layers of sand, 

 having such markedly different character- 

 istics, would seem to point clearly to rather 

 different origins. The factors and forces con- 

 tributing to their formation can hardly be 

 said to be identical. The material of the ' 

 white layers suggests rounding, pitting, sort- 

 ing, and deposition by the wind. The ma- 

 terial of the brown layers has evidently been 

 water-worn and water-borne, coming from a 

 comparatively distant region. The occur- 

 rence of these different layers with their im- 

 plied differences in origin and deposition may 

 well suggest something of the Jiistory of this 

 region, especially in regard to the extent and 

 frequency of rainfall. 



As these rocks contain no fossils, and in 

 their general lithological character point to 



