24 W. Cross — Post- Laramie Deposits of Colorado. 



physical appearance from the beds of the Laramie. Above 

 these are unquestioned Wasatch beds.* 



South Park. — Near Como in South Park, Colorado, Mr. 

 Hills has found a very remarkable formation which will be 

 best described in his own language : " While recently en- 

 gaged in the examination of the small Laramie area in the 

 South Park basin, I there observed unquestionable evidence 

 of a former grand eruption, of a character not previously noted 

 in that part of Colorado. The evidence consists in the occur- 

 rence of thick sheets of eruptive conglomerate, intruded 

 partly into the marine Cretaceous and partly into the Laramie, 

 to some extent above the workable coal. These sheets are 

 continuous from Mine No. 5 near Como to the southern limit 

 of the Laramie beds,, a distance of fully fifteen miles, beyond 

 which I did not trace the exposures. About three miles south 

 of Mine No. 5, the intrusions above and below the coal beds 

 coalesce and form a body of conglomerate several hundred 

 feet thick completely cutting out the workable measures for 

 nearly a mile. The material consists of rounded pebbles and 

 bowlders of andesite embedded in a matrix of finer material 

 of similar composition." ..." The material itself may be re- 

 garded as the product of intense dynamic movement, probably 

 brought to the surface as a hot conglomeritic mud, or in a 

 condition to produce an explosive eruption, whenever, owing 

 to diminished pressure, the contained water flashed into 

 steam." . . . " The material then thrown out and scattered over 

 the surface would be in a condition to be transported in large 

 quantities to the nearest area of sedimentation — the Denver 

 basin — and presumably at the very time when the Denver beds 

 were laid down." f 



It seems to the writer that the character ascribed to the 

 South Park eruption is so novel and its extent so far a matter 

 of speculation that it can at present hardly enter as an 

 important factor into the question as to the origin of the 

 eruptive materials of the Denver beds. The facts concerning 

 the constitution of the Denver beds given in the original 

 article do not allow of the adoption of Mr. Hills' suggestion. 

 They demand a source near at hand and one whose location 

 shall explain why eruptive material practically excludes 

 Archaean material in fine, slowly deposited sediments, close to 

 an Archaean shore-line. 



Canon. City. — In his address Mr. Hills refers to remnants 

 of a formation near Cation City which seems related to the 

 Denver formation. Through his kindness in personally com- 

 municating the news of his discovery, my colleague, Mr. G. H. 

 Eldridge, was enabled in the season of 1890 to hurriedly 



* Op. tit., p. 3S9. f Op. tit.,, pp. 393, 394. 



