206 KANSAS CITY REVIEW OF SCIENCE. | 
About Silver Cliff and Rosita are extensive Trachyte, or light colored lava | 
rocks, bearing mineral. ‘These extend for ten miles nearly east and west; and | 
evidently consist of various outpours differing in their appearance and minerals. | 
Their geology and relations are an interesting field of study. | 
Perhaps the latest is that on which Silver Cliff is built, which bears a pecul-| 
jar manganese ore carrying free milling chloride of silver, of the Racine Boy type: | 
this appears over an_area of two miles east to west, and a mile and-a-half north to 
south. It has a black and glossy pitchstone core exposed at various places under it. 
North-west of this is another body, rather larger, and to the south-east about | 
Rosita another still larger, which are probably older, different in appearance and | 
with different minerals, iron, lead, zinc, copper, sulphurets, and manganese, with | 
silver diffused through the rocks, and in more or less defined leads. All these | 
carry silver in small quantities, making a wonderful field for future mining, from | 
the immense quantity of the rock and its accessibility. After the melted trachyte | 
was outpoured and by cooling left fissures and deep cavities, no doubt water 
penetrating the deep recesses of the earth was heated and caused to take up mine- 
rals in solution and bring them to the surface, where on cooling they were deposi- 
ted in various forms in the passages and through the broken and porous trachyte. 
The Bassick and Bull-Domingo mines are of this type distinctly, while no 
doubt lesser and more diffused outruns have produced the minerals throughout the 
trachyte beds. This trachyte is very old, as shown by hundreds of feet of denu- 
dation and ravines cut in it, especially toward Rosita. There isa sedimentary 
formation, which I have named the Eositon, five miles north-east of Silver Cliff, 
formed from washings of these old trachyte beds and the granite east. This extends 
for-miles in a line from Dora to Bassick’s, in the bed of an old stream, half mile 
wide. Modern streams havecut down showing nearly a hundred feet in thickness. | 
The strata are mostly soft, some fine grained and some coarse with gravel; often 
of soft talc-like nature. At one place, west of Cafion road it is capped with a lo- 
cal deposit of limestone, containing granite boulders, valuable for lime. 
Half mile west of Apperson’s mill the upper strata contain quantities of fos- 
sil wood, of many familiar kinds, apparently showing the grain finely. No ani- 
mal remains have yet been found in it, but it may contain wonders of the time 
when the monsters roamed this land, whose bones were found by Profs. Marsh, 
Cope and Mudge, twenty-five miles north, at Prospect Park. ‘There isa stratified 
sand formation overlying the trachyte north and west, which shows the presence 
of a body of water at a late age nearly as high as the city, at least. | Animal re- 
mains, with huge teeth, have been found in this, in the shaft of the St. John claim 
two-and-a-half miles north-west. There is a deposit of coarse and fine worn gra- 
vel for twenty-five miles south and ten miles wide sloping into Grape creek valley, 
which may be known as the Wet Mountain Gravels. 
There are indications of Glacial action extensively in this region, and no 
doubt. these gravels owe much to it. Debris of the Racine Boy type of ores is 
scattered over the hills for miles north-east. 
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