Intelligence and Miscellaneous Articles. 451 



tain-formation. I have nothing to say on this thesis, but I wish to 

 draw attention to what I conceive to be a mistake in his view of 

 Appalachian structure. Great chains, as we all know, consist 

 usually of a granite or metaraorphic axis flanked on either side by 

 tilted and often crumpled strata. Now Mr. Eeade seems to think 

 that the strata were pushed back and crumpled by the protruded 

 axis. The Appalachian seems inconsistent with this view, but Mr. 

 Eeade thinks only seemingly so, because the crumpled strata on the 

 eastern flank have been completely carried away by erosion. 



'Now American geologists believe they have good reason to think 

 that the metamorphic region of the Appalachian does not belong 

 to the Appalachian chain proper at all, but existed as land long before 

 the Appalachian was born, viz. at the very beginning of the Palaeo- 

 zoic Era. The evidence of this is, that the very lowest Palaeozoics 

 lie everywhere unconformable on the eroded edges of the crumpled 

 Archaean, and even the outlines of the old Cambrian shore-line 

 can be traced. The Appalachian was not formed until the end of 

 the Palaeozoic. 



Perhaps it may not be amiss to call attention also to the struc- 

 ture of the coast-range of California. It is strongly crumpled, 

 with at least five anticlines and corresponding synclines *, and yet 

 in many places no sign of a granite or metamorphic axis. 



Very truly, 



Berkeley, Cal., Joseph LeConte. 



March 29, 1888. 



ON THE ACTION OF LIGHT ON THE ELECTRICAL CONDUCTIVITY 

 OF THE HALOID SALTS OF SILVER. BY SVANTE ARRHENIUS. 



Two parallel silver wires were coiled, at a distance of 2 millim., 

 about a rectangular glass plate (4x5 centim.), then painted with 

 an ammoniacal solution of chloride or bromide of silver, and slowly 

 heated until the water and ammonia had evaporated, so as to form 

 a thin skin of chloride or of bromide of silver. The plate was 

 covered with a screen with a slit 1 centim. in breadth, and there- 

 upon placed in various parts of a spectrum 7*2 centim. in length. 

 The silver wires were introduced into the circuit of a battery of 

 40 Clark's elements, in which was a very sensitive reflecting- 

 galvanometer (1 div. =7x 10 -11 amp.). Without illumination the 

 galvanometer gave a constant deflection. With illumination this 

 was greater, but returned to its former value on darkening. When 

 the width of the slit which produced the spectrum was respectively 

 0-60, 0-473, and 0-24 centim. in breadth, the action of the light for 

 each part of the spectrum was proportional to the intensity of the 

 light. Por the various colours, the action increased from the red 

 to the line Gr, first of all slowly, then more rapidly, and sank then 

 to the ultra-violet in the reverse direction. The action is thus not 



* Amer. Journ. Science, vol. ii. p. 297 (1876). 



