La Salle, III., December 1M1, 1.S75. 



Dear Sir: I have to-day forwarded to you, by express, the manuscript of my 

 geological report of your exploration of 1858-59 (two copies), which you liad the 

 kindness to send me for revision. 1 have made no essential changes or corrections, but 

 have only struck out some passages which, at this date, appeared to me irrelevant or 

 out of place. I was inclined to shorten the report materially, but this would have 

 necessitated a rewriting of a large portion of it. 



In returning to you the report I have to say that I was much pleased to find that 

 I had really no cause to make any essential corrections. When this exploration was 

 made, the country over which it extended was virtually for the most part a wilderness, 

 partly then trodden for the first time by the foot of the white man. Its mineral wealth 

 had then not been discovered. Now the whole of it is spanned by the iron rail, with 

 many branch roads leading into its distant valleys. It is teeming all over with human 

 industry. The open country has become the domain of the farmer and stock-raiser; 

 numerous coal-mines have been opened at distant points; every mountain and gulch 

 has been explored by the omnipresent miner; steam batteries thunder in its most 

 distant mountain recesses, crushing the ores of the precious metals; and cities have 

 sprung into life and prosperity where then only the squalid Digger Indian hunted the 

 ground-rat. Then the geological exploration was confined to a naturally incomplete 

 reconnaissance within reach of a military escort. Since then, splendidly-equipped 

 geological exploring parties have spent years in closely examining the whole district. 

 Numerous scientists have spent the summer seasons rusticating in the mountains, while 

 mining engineers have professionally traversed it in every direction. 



Under these circumstances, the interest with which some parts of this report would 

 -have been received at the time when it was written, does, of course, not any longer 

 attach to it. It is, in fact, superseded; but its perusal will show that while it is neces- 

 sarily fragmentary and incomplete, it represents the general outlines of the geological 

 structure° of the country pretty correctly, and contains many diligently-compiled 

 details. In consequence of the non-publication of the report, the credit due to it has, 

 in various instances, been claimed by later observers. In revising the report for pub- 

 lication, I have therefore abstained from making any essential alterations, preferring 

 to let it stand on its merits such as it was originally written, merely eliminating some 

 too lengthy remarks. 



I am, dear sir, your obedient servant, 



IIexkv Engelmann, 



Mining Engineer. 



General J. H. Simpson, 



Colonel of Engineer*, U. S. A., Saint Louis, Mo. 



