OF ARTS AND SCIENCES. 107 



coke is almost entirely free from volatile or bituminous mat- 

 ters, being less puffy than ordinary coke, but less compact than 

 anthracite. In the vicinity of the coal-seams are dikes of trap- 

 rock. One hundred and twenty feet below the surface there 

 is a bed of trap-rock, twenty-five feet in thickness ; below this 

 is a clay-slate, almost vitrified, commonly called " basalt," 

 which has assumed a columnar crystallization ; below this are 

 alternating beds of sandstones and slates. Then, at the depth 

 of sixty feet below the trap, there are ten or twelve feet of this 

 coke, having occasional traces of vegetable remains, and at the 

 bottom of the bed having a small amount of bituminous matter. 

 Twenty feet below this is a half-coky coal, and fifteen feet 

 below this, the ordinary bituminous coal of the country. 

 These strata plainly indicate the graduation and diminution 

 of the heating action in a downward direction. It is very 

 curious, that in the beds of carboniferous slate above the trap 

 there is no indication of this metamorphic action ; there are 

 even seams of coal above it ; the veins of injected material 

 must have been thrown up from beneath, the heating action 

 extending from the interposed trap in a downward direction- 

 This series of strata is therefore interesting, as proving that 

 there were periods of igneous activity during the deposition 

 of these formations. 



Three hundred and ninety-eiglitli meetingi 



April 11, 1854. — Semi-Monthly Meeting. 



The President in the chair. 



Professor Levering exhibited a model of an instrument for 

 producing great velocities in experimental physics, particularly 

 in optics. The motion is produced by a spring acting upon 

 a train of wheels, and may be very suddenly diminished or 

 increased by friction. With it were performed several experi- 

 ments by the rapid revolution of variously painted cards ; as 

 of mixing the prismatic colors, and any two complementary 

 tints or colors to form white. The instrument is of practical 



