REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1901 r21 



below the point to which explosive products may have fallen 

 back in the volcano there to become embedded in still hot lava. 

 Certainly the gross structure of the rock recalls many lava 

 sheets with locally formed explosive products, and the same 

 structure is to be observed in the lava flows of the Newark 

 formation of Triassic age in the Connecticut valley 1 (fig. 3). The 

 accompanying photograph, plate 5 of the walls of Stark's Knob 

 shows the general structure. 2 



The fragment shown in figure 2, lying south of the fault, is 

 more massive than the main stock, and the ground mass 



Fig. 3 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, devitri- 

 fied, volcanic glass surrounding the lava balls. 



approaches more nearly the dense, dark basalt, but here are 

 also developed amygdules. 



A hand specimen obtained here displayed fairly coarse cry- 

 stals of plagioclase, 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 prod- 

 ucts makes Stark's Knob one of the most interesting igneous 

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



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 Ct, see Davis, "W. M., 

 The Lost Volcanoes of Connecticut. Pop. Sci. Mo. 1891, p. 221, fig. 1; 

 U. S. Geol. Sur. 18th Rep't. 1898. pt 2, p. 65. 



2 These views were obtained for the museum by Messrs H. C. Magnus 

 and H. P. Whitlock. 



