July 27, 1917] 



SCIENCE 



93 



corresponding decrease in thickness of the 

 white layers is found, on the average, follow- 

 ing every tenth or eleventh layer. 



This recurrence, as observed at a number 

 of places on the quarry walls, as well as on 

 detached fragments, ranges from the sixth to 

 the fifteenth white layer. For example, at 

 one place (Quarry "A," Section I.) the 

 writer measured the thickness of the series of 

 white layers, tlie thickest layers recurring as 

 follows: seventh, eleventh (from and includ- 

 ing the seventh), fifth (or fifteenth from the 

 seventli), eleventh, ninth, fourteenth. At 

 Section II., Quarry " A" the thickest white 

 layers recur as follows: ninth, seventh, sixth. 



1, Section I., Quarry " A," to the top of 

 column 4, same section, there are a total of 

 33 white layers. In the section from Quarry 

 " B," from the layer at the top of column 4 

 to the top of column Y, there are 34 white 

 layers; from the top of column 7 to the top 

 of column 11, there are 34 white layers. Like- 

 wise, from the top of column 2 to the top of 

 column 6 there are 40 white layers ; from the 

 top of column 6 to the top of column 10 there 

 are 38 white layers. 



It may be that it is just by chance that 

 these layers are arranged in this way, yet the 

 agreement with known climatic pulsations is 

 so striking as to make one ask whether it is 



"B," Section I 



White Layer 



Fifteenth 



Fourteenth... 

 Thirteenth ... 



Twelfth 



Eleventli 



Tenth 



Ninth 



Eighth 



Seventh 



Sixth 



Fifth 



Fourth 



Third 



Second 



First 



6 (top) 

 13 

 IS 

 10 

 10 



8 

 {10) 



At another place (Quarry "B"), about a 

 quarter of a mile away, the following periods 

 were observed: tenth, twelfth, tenth, seventh, 

 eleventh, fifteenth, tenth, twelfth, sixth, thir- 

 teenth, sixth. These three sections are about 

 2.5, 2 and 4 feet in thickness, respectively. 

 The details of these measurements are shown 

 in the tables above. On about 18 quarried 

 fragments it was found that on the average 

 every eighth to twelfth white layer was thicker 

 than those between. On several such frag- 

 ments, this recurrence was observed as fol- 

 lows: eleventh; tenth; eleventh and following 

 ninth; eighth; ninth and following eleventh; 

 tenth. 



Another striking periodicity may be noticed 

 in the tables. These periods correspond 

 rather well to the average number of years in 

 the Briickner cycle, as from the top of column 



just chance after all, or a result of natvural 

 laws. It is quite evident that the recurrence 

 of layers of a certain character is periodic. 

 Whether one can in this manner safely assign 

 a limit to the yearly deposits seems question- 

 able, but one may certainly inquire into the 

 probabilit.y of deducing from a study of these 

 variegated sandstones the conclusion that at 

 the time of their formation the climatic con- 

 ditions, especially with reference to rainfall, 

 were fluctuating much as they have been 

 within recent times. 



It would be distinctly interesting to know 

 whether geologists can find, in more exact and 

 complete studies, further evidence of pulsa- 

 tory changes of climate having been recorded 

 in the clastic rocks. C. E. V.ul 



Colorado Agricultural Colleqe, 

 Fort Collins 



