486 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



mucli diminished sotde lioweverj the undisturbed Randstones reaching within 

 twenty feet of the trap. On all other of these streams, the sandstone is undis- 

 tui-hed. The explanation which first suggests itself to account for these dis- 

 turbances is naturally, that they were caused by the ejection of the traps 

 through the already formed sandstones. In answer to this it may be said that 

 it is very difficult to see how just such a disturbance as this could have been 

 caused in this way, the sandstones presenting no appearance of baking or other 

 indication of heat, but seeming rather to ha^ve been crushed by a pressure from 

 the south. Next the trap it is crushed to a confused mass, a. little further a 

 few layers of sandstone become distinguishable, Btill further these are all dis- 

 tinct but broken and pitching in every direction, and finally they grade into 

 regular unbroken horizontal layers. It may also be said that the proofs 

 alrea^ly given of the greater age of the copper bearing rocks, as compared with 

 the horizontal sandstones are so strong as to necessitate some explanation of 

 these disturbances other than the one just mentioned. The oidy one that I 

 can offer, is this ; the traps being deep seated are, as it were, independent of 

 the more superficial sandstones, and would, if impelled to move Ijy any force, 

 move independently of them. Now a very slight movement of the traps north- 

 ward against the sandstones would produce ail the phenomena observed. Such 

 a movement is not at all diificult to explain." (Sec also Am. Jour. Sci., 1874, 

 (3) VIIL, pp. 46-56.) 



In 1879 Professor Irving adopted, in part, a difiTcrent mode of ex- 

 plaining the phenomena observed above. He remarks : — 



" It appears that at the contact there is in many cases a confused brecciated 

 mass of sandstone and crystalline-rock fragments, some of which are of great 

 size, while in places they become rounded, and the rock passes into the ordi- 

 n.ary conglomerate. These peculiar appearances, oidy in one case reaching to 

 any considerable distance from the crystalUne rocks, are to be attributed in the 

 first place to the naturally confused mode of deposition on the cliffy shore of 

 the waters in which the sandstones were originally deposited, but, as I have 

 shown in another place, a slight movement northward of tlie deep-seated crys- 

 talline rocks against the more superficial sandstone would account for much. 

 Another thing tending to confuse would undoubtedly be the chemical action, 

 which, as is well known, is so apt to be set up with unusual energy along 

 the contact of dissimilar formations." (Geol. of Wise, 1880, III., pp. 17, 



307.) 



Mr. E. T. Sweet, in his report in the same volume, (p. 337, see also 

 pp; 349, 350,) states in regard to the same phenomena, that "on Mid- 

 dle river, tlie original lines of deposition have been entirely obliterated, 

 and the very argillaceous sandstone transformed into a transverse cleav- 

 ing slate, somcwliat micaceous." Tjiia shows the incorrectness of Pro- 

 fessor Irving's statement that the sandstones present ^'no appearance of 



