SUPPOSED JURA-TRIAS OF THE FRONT RANGE OF COLORADO. 495. 



volcano, as the Zeolites to this thickness could only come from the long wearing 

 away of the Mountain of Basalt. Our volcano, however, was not dead yet, as 

 following the conglomerate is a thin bed of sandstone, volcanic ash, most beauti- 

 fully lined in alternate bands, very fine and thin, and telling us that it was the 

 last dying throes of one of Nature's giants. 



Along the line of this strata it would be quite natural, after what had been done 

 by this volcano, to expect a line of weakness, which broke as the Rocky Mountain^ 

 system arose and made a fault between Table Mountain and the Front Range. 

 Here the sedimentary strata tilted up and the volcanic eruptive record was pre- 

 served ; but east of Table Mountain the rocks are all eroded out of what is now 

 the Platte River basin. I could only get this representative section straightened 

 out when I gave up the idea of the Jura-Trias existing here at all. 



Again. Professor Rogers, in his admirable Surveys of Pennsylvania, accounts 

 for the depositing of the Triassic of the Atlantic slope, as a deposition of river 

 silt, the waters of which were possibly more or less affected by tides; that this 

 river extended from the New England States in the north down what is now the 

 Atlantic slope to Georgia, the deposit culminating in its greatest thickness in Vir- 

 ginia. I cannot find evidence for an analogy to this in the Colorado Front 

 Range. 



The characteristic fossil representations of the Trias of the Atlantic slope 

 are the foot-prints occurring in the sandstone bordering the Connecticut River of 

 which over 12,000 tracks have been found, averaging 100 tracks for each individual 

 animal known. Comparative anatomists are agreed, that these are the foot-prints 

 principally of reptiles or cold-blooded animals. This fact is used by geologists to 

 illustrate the theory of evolution as evidenced by the geological formations of the 

 diifferent periods of the earth. In a lecture in Denver some months ago this sub- 

 ject was clearly and beautifully treated by Professor W. D. Gunning, of Boston, 

 (such theories appear to be his strong forte). To the attention of this gentlemen 

 I presented a discovery of my own, made a short time before his arrival, in some 

 sandstone flagging put down on i6th Street in Denver. The discovery was made 

 in April, 1882, and consists of three distinct sets of foot-prints, made evidently 

 by three different animals. 



Professor Gunning verified them as foot-prints on the spot, and this I believe 

 to be the first recorded discovery of the kind. They are in the sandstones of the; 

 St. Vrain quarries of the Front Range of Colorado. 



The largest foot-prints were evidently of an animal going at a leisurely gait 

 across the wet sands, leaving a record as distinct and perfect as a fox would un- 

 der similar circumstances in a snow-field. One of the smaller sets have the whole 

 four feet drawn together, as if the animal had just alighted after a spring, and 

 paused a moment to listen and see if the cause of his alarm still continued. Af- 

 terward, in the stone-yard, I found one large slab with just two tracks upon it,, 

 similar to the ones first mentioned, but impressed by an entirely different action. 

 Instead of a leisurely trot, he had been in a hurry, and had in his jumps come; 

 down upon the wet sand heavily ; as he sprang forward his nails scratcfhed deep^- 



