Pant X.] + UNCONFORMABILITY. | 599 
influence on the precipitation of mineral matter in the fissures passing 
through them. But that this mineral matter came chiefly from below 
appears almost certain. The phenomena of the ascent of hot water 
in voleanic districts afford a close analogy to what has occurred in 
mineral yeins. It is known that at the present time various 
minerals, including silica, both crystalline and calcedonic, and various 
metallic sulphides, are being deposited in fissures up which hot water 
rises. At the same time it is conceivable that to some extent there 
may be a decomposition of the rocks on either side of a fissure, and 
that a portion of the mineral matter abstracted may be laid down in 
another form along the walls of the fissure, or, on the other hand, 
that the rocks on either side of the fissure may be permeated for 
some distance by the ascending waters, and that some of the mineral 
substances carried up in solution may be deposited in the pores and 
cavities of these rocks as well as in the fissure itself.’ 
Part X. UNCONFORMABILITY. 
Where one series of rocks, whether of aqueous or igneous origin, 
has been laid down continuously and without disturbance upon another 
series, they are said to be conformable. ‘Thus in Fig. 311 the sheets of 
conglomerate (bb) and clays and shales (¢ d), have succeeded each 
other in regular order, and exhibit a perfect conformability. They 


Fig. 311.—UNcCONFORMABILITY AMONG HORIZONTAL STRATA. LIAS RESTING ON 
CARBONIFEROUS LIMESTONE, GLAMORGANSHIRE (B.). 
overlap each other, however, each bed extending beyond the edge of 
that below it. As already explained (p. 495), this structure points 
to a gradual subsidence and enlargement of the area of deposit. 
But all these conformable beds repose against the older platform a a, 
with which they have no direct connection. That platform may 
consist of horizontal or inclined clastic strata, or contorted schists, 
or eruptive massive rocks. In any case there is a complete break 
between it and the overlying formation, the beds of which rest suc- 
1 See J. A. Phillips, Q. J. Geol. Soc. xxxy. p. 390. 
2 Henwood, Address Roy. Inst. Cornwall, 1871. J. A. Phillips, Phil. Mag. Nov. 
1868, December 1871, July 1873, March 1874. J. 8S. Newberry, School of Mines 
Quarterly, New York, March 1880. J. A. Church, “The Comstock Lode,” 4to. New 
York, 1879. Sterry Hunt, “ Chemical and Geological Essays,” 1875, p. 183. Brough 
Smyth’s “ Goldfields of Victoria,” Melbourne, 1869. 
