392 THE POPULAR SCIENCE MONTHLY. 



Go out on the flank of the fold, and find the bed of rock which 

 woukl form the summit of the great wrinkle, had there been no 

 erosion, and there sink a shaft 24,000 feet, and you will be able to 

 study a certain succession of beds of sandstones, shales, and lime- 

 stones. Go two or three miles farther from the mountains, and sink a 

 shaft; the first 8,000 feet or more will be through sandstones and 

 shales, unlike those seen in the first section ; then you will strike the 

 summit of the first section. Continuing down for 24,000 feet, the first 

 will be reproduced, stratum for stratum. Now start on either side of 

 the fold, and cross to its centre ; and you will pass over the same 

 series of strata in the same order as you would in descending the first- 

 mentioned shaft, and in the second also, b'elow the upper 8,000 feet. 

 Now pass again from the centre to the flank of the fold, in either 

 direction, and you can study the same rocks in the same order as you 

 would in ascending these shafts. It will thus be seen that in these 

 truncated wrinkles we are enabled to study geological formations 

 without descending into the depths of the earth. 



Fig. 1 has been constructed for the purpose of graphically ex- 

 pressing some of the important facts observed in the great Uinta 

 Fold. In this, the beds are seen to turn up in a great flexure, and to 

 be cut away above, the higher beds more than the lower; thus 4, 4-4, 

 4, has been cut away much more than 5, 5-5, 5; and 10, 10-10, 10 

 has suffered much less erosion than the beds above it. The only place 

 where the water has carried it away is at Y, the bottom of the caiion. 



In this diagram, the line A-B represents the lowest line of ob- 

 servation, as exhibited in the bed of the river. All below this line is 

 theoretical. The line C-D represents the level of the sea. The 

 stratum ^, JE-E, E was the last deposited antecedent to the com- 

 mencement of the emergence of the summit of the fold. Had there 

 been no erosion of the fold, the beds intervening between the broken 

 line I, I, I (which is a continuation of the lines E, E-E, E), and the 

 irregular line which represents the surface of the country, cutting the 

 edges of the eroded beds, and passing through the lowest. No. 10, at 

 Y, would still be found, but they have been carried away. 



The diagram does not properly represent the entire amount of 

 erosion, from the fact that the vertical scale is exaggerated, and the 

 beds have been extended beyond their proper limits, for the jDurpose 

 of representing more clearly other facts of interest. 



It will be seen that in passing along the line A-B (the bottom of 

 the river-channel), from the shaft -^to the bottom of the canon Y^ we 

 are able to observe the beds 4, 6, 6, 7, 8, 9, 10, in the same order that 

 we would in descending the shaft F. The beds 1-1, 2-2 have been 

 deposited since the emergence of the summit of the fold, and hence 

 never extended quite across it ; yet the lower members of these beds, 

 doubtless, at one time extended much farther up on the flanks of the 

 fold. They have been cut away, however, as represented in the dia- 



