|:;1 j. s. i»ii.i.i:i: — ujdstone dikes 



It is well known thai all rocks a short distance beneath the Burface, within 

 the accessible portion <>t' the earth's crust, contain water, and thai the amount 

 that each contains is in a general way proportional to its porosity. It is 

 evident, therefore, that the loose Band which filled the fissures from below, 

 being very porous and hounded chiefly by shahs which have a much Lower 

 degree of porosity, must have I. ecu saturated with water. 



It appears that if by any means a fissure wen- suddenly formed from the 



surface down to the sand saturated with water the latter would rise in the 



fissure and. it* the hydrostatic pressure wen- sufficiently great, the water 

 would rush forth, carrying the sand with it to till the fissure ami. like an 

 artesian well, overflow upon the surfai 



With a view to determining the possible influence of the fractured strata 

 in filling the fissures, -Mr. d. Stanley-Brown made for me the Beries of specific 

 gravity determinations noted in the following table: 





Specific Gravity of Dike and J>>>l Rocks. 



Shales penetrated by the dikes — 



Dry creek, at A. Allen's .... 2.7346 I „ _., 



North fork of Cottonwood, 1 mile above Oaa Poinl 2.7874 | ' 



Sandstones or beds — 



Dry creek. :; miles west of A. Allen's. ._. 2 '.Tor, *\ 



i on Middle fork, I mile above Miller's 2.68 67-50 



in Byron gulch, l mile above Ono. 2.6620 



- \ N DSTON BS ok Di k Ks — 



Fight gulch 2.68 I 



Dry creek, 1', miles above mouth of Salt creek - - 



" " •■ ■■ by the road 2.6746 



Three-quarters of a mile up Middle fork from filler's .. 2.7006 | 



North fork of ( Jottonwood, ■; mile below mouth of Eagle creek *_'.i','.i \Q 



'I'he specimens used in the determinations were cut and ground in the form 

 of cubes with round edges, and at the beginning ami end of' the observation 

 were dried to a constant weight. The weighings were made directly in water 

 by means of a tine wire Bupporl and the result reduced, according to Kohl- 

 rausch's formula, to \ < '. 



'I'he sandstone of the dike- appears in the average to he slightly heavier 



than that of the beds a fact w inch may he dim to the greater a hum la nee of 

 biotite in the dike rock-. At the time the fissures were filled, however, the 



loose -and must have had a lower Bpecific gravity than now. lor the spaces 

 between tin grains which were tilled by water or air are now occupied by 

 carbonate of line-. 'I'he -hah- are appreciably heavier than the sandstones, 



and, -inee they ( StitUte tie g] ". :H ma-- of the c.iiutry lock of the < 1 i k • B, 



by tlcir weight alone they may have aided in forcing the watery -ami into 



