East Haven- Branford Region. 377 



shown that the absence of extensive baking of the contiguous 

 strata would not alone prove much regarding the heat of the 

 trap. Furthermore, as heat is propagated more readily in the 

 direction of the strata than perpendicularly to them, the con- 

 solidating effect of a mass of trap lying conformably upon the 

 sandstone would not be apparent as far from the contact as it 

 would from trap intersecting the strata. 



The amygdaloidal or, rather, the vesicular structure of erup- 

 tive rocks is supposed to have been produced wherever diminu- 

 tion of pressure allowed the highly heated water contained in 

 their mass to expand into steam. The most favorable place 

 for the production of vesicular lava is the upper part of a sub- 

 aerial flow ; but that the formation of vesicular lava, or trap, 

 has not been confined to subaerial or subaqueous flows has 

 been proven by the amygaloidal character of some of the dikes 

 in the first and third ranges west of Pond Hock. The six inch 

 band of amygdaloid at the botom of the main trap sheet can 

 not be used as an argument either way, for it can be explained 

 easily whether the trap be intrusive or extrusive. 



The " irregular and brecciated " structure of the ridge is 

 best shown at the junctions between the first and second and 

 the second and third parts of it, and is not well developed 

 anywhere else. Such a structure would be produced by the 

 sudden cooling of liquid rock, and is frequently found near 

 the walls of anhydrous as well as of hydrous dikes and in- 

 trusive sheets. Decomposition has been more extensive in the 

 hydrous trap than in the other, which brings out the structure 

 more plainly. A low dike about 1 30 feet wide is exposed on 

 Farren Avenue, Fair Haven, the rock of which is as much 

 broken and decomposed as that at the lake. This is distinctly 

 a dike, the strata across which it cuts being exposed on each 

 side of it. This " brecciated structure," therefore, being pro- 

 duced by local conditions, proves nothing with regard to the 

 intrusive or extrusive character of a trap sheet. 



The " alteration and hydration " of the Fond Rock trap is 

 Prof. Davis's fourth argument for the extrusive, or overflow, 

 character of the sheet. The alteration of the rock of this 

 ridge varies greatly in degree, in different places. At the foot 

 of the lake and at the railroad cut, decomposition has gone so 

 far as even to destroy the crystalline texture of the rock, but 

 the trap of most of the ridge is dense, tough and sublustrous 

 and shows its crystalline structure plainly, though much 

 chlorite is present. Slide No. 23 is from the middle of the 

 sheet on the northern hook of the ridge. The Farren Avenue 

 dike is thicker than the Pond Eock sheet at either the wagon- 

 road or the railway crossing and is much decomposed through- 

 out its mass; and many of the dikes and intrusive sbeets 



