202 A. J. TIEJE 



Fountain sediments, grinding the feldspar and muscovite to minute 

 fragments and rounding the quartz grains to their unusual uni- 

 formity of size and sphericity. Since there would have been a 

 limit to the depth of such wind work, though none to the amount 

 of comminution, the sharp contact of Fountain and Lyons is 

 accounted for reasonably. The very fine irregular cross-bedding 

 on the laminae is such as may be observed on fine, modem sand 

 layers. The large-scale cross-bedding, dipping in two opposite 

 directions at gentle angles, may well have been that of sand dunes, 

 whose topmost layers are truncated as the winds change direction. 

 The uppermost sands, too, are whitest, as if protracted whipping 

 about had removed some of the ferric oxide film. The local con- 

 glomerates may have been due to rare, vehement floods from the 

 distant highlands; the boulders are rounded, as if they had moved 

 far. Even the sporadic amphibian tracks and the occasional 

 obscure ripple marks are consistent enough with the hjrpothesis.^ 



There would seem to be, then, a kind of unconformity between 

 the Fountain and Lyons sediments — an unconformity, curiously 

 enough, for which Butters' view of the "Ingleside" would call. 

 But the unconformity would be of an unnamed type, for the record 

 of what happened is not lost. The record takes the form of a 

 geologic palimpsest, as it were — Lyons history being superscribed 

 upon erased Fountain history. 



Interpretation: climate and paleogeography. — ^Lyons climate has 

 already been interpreted as dryer than that of Fountain time. As 

 to relation of land and sea, all that can be predicated is that, as 

 Pennsylvanian time continued, marine or semimarine conditions still 

 prevailed to the north of Colorado, and probably to the east. 

 Western highlands were lowered. 



^ C. E. Vail, "Lithologic Evidence of Climatic Pulsations," Science, Vol. XLVI 

 (1917), pp. 91-93, has preceded the writer's point of view by simply stating that the 

 Lyons is eolian, though he has not dealt with its larger problems. In fact, he confines 

 himself to one interesting suggestion. That alternation of light and dark laminae 

 which has been noted he views as the testimony to "climatic pulsations." The 

 "white" laminae he describes as comprising "very well-rounded grains of white quartz, 

 with scattered specks of iron oxide," and the "brown" laminae as being composed of 

 "angular and subangular" grains, with coatings of iron oxide." The brown laminae 

 are then ex-plained as laid down by torrential rains on a desert, the white laminae as 

 being purely eolian. The distinction between the grains of the laminae has perhaps 

 been overemphasized. 



