Il8 NEW YORK STATE MUSEUM 



of Triassic age in the Connecticut valley^ (figure lo). The accompanying 

 photograph, plate 17 of the walls of Stark's knob shows the general 

 structure. 



The fragment shown in figure 9, lying south of the fault, is more massive 

 than the main stock, and the ground mass approaches more nearly the dense, 

 dark basalt, but here are also developed amygdules. 



A hand specimen obtained here displayed fairly coarse crystals of plagio- 

 clase, indicative of an intratelluric origin, such as are common in the diabase 

 of many dikes. This combination of the characteristics of dike rocks and of 

 effusive explosive products makes Stark's knob one of the most interesting 

 igneous occurrences, small as it is, within the limits of the State. 



Jointing of the lava crusts. The surfaces of the lava balls are beset with 

 a network of cracks perpendicular to the surface. On exposed w^alls the lava 

 crusts frequently fall to pieces in short, polygonal joint columns similar to 

 basaltic columns. 



Fig. 10. Sketch of a portion of the western wall of Stark's Knob, showing 

 the gray, scoriaceous interior of the lava balls, the basaltic, jointed crust, and 

 the fissile, devitrified, volcanic glass surrounding the lava balls 



The inclusions of limestone point to an irruption through the lower 

 Paleozoic limestones which must occur in this field beneath the Hudson 

 terrane^ The inclusions may be appealed to as evidence that the trap came 

 up through the Silurian and subjacent terrane, as held in this paper, and that 

 the rock is not to be regarded as an in-faulted remnant of a lava flow once 

 covering the Hudson terrane in this vicinity. 



Since Woodworth's study o£ the knob, the rock has been utilized 

 for various purposes and largely quarried away. We visited it 

 in 1910, in 191 1 and in 1912. In 1910 active quarrying was in 

 progress; in 191 1 this was not the case but much material had 



I 

 I 



^Emerson, B. K. Diabase Pitchstone and Mud Enclosures of the Tri- 

 assic Trap of New England. Geol. Soc. Am. Bui. 1897. 8:59-96. For an 

 illustration of the ball structure at Meriden, Conn., see Davis, W. M., The 

 Lost Volcanoes of Connecticut. Pop. Sci. Mo. 1891, p. 221, fig. i ; U. S. Geol. 

 Sur. i8th Rep't. 1898. pt 2, p. 65. 



