Jura-Trias trap of the New Haven Region. 167 



From the facts we are safe in concluding that the liquid 

 rock of the little fissure had at its outflow the maximum tem- 

 perature of the main mass ; for it was from its lower portion. 

 Evidence of high heat is indicated by the presence of olivine. 

 For in the experiments of Fouque and Michel Levy, basalt 

 on cooling after being for 48 hours at white-red fusion, " a 

 temperature above the melting point of pyroxene and labra- 

 dorite," afforded " crystals of olivine in a brownish vitreous 

 magma ;" but on cooling from cherry-red fusion sustained for 

 48 hours, afforded numerous microlites of labradorite and 

 augite with magnetite.* 



The olivine of the dike was made at the expense evidently 

 of the pyroxene ; and as ordinary olivine contains 8 to 10 per 

 cent of iron protoxide and 41*5 of silica, and the pyroxene of 

 "West Rock trap, according to the analysis of Hawes,f 15*3 per 

 cent of the former to 50 "7 of the latter, some iron protoxide 

 may have been set free in the process to add to the magnetite, 

 besides silica to form the quartz-crystals and silicates in cavi- 

 ties or fissures. 



The aphanitic texture of the trap indicates rapid cooling, 

 and its vesicular character, cooling where there was much 

 moisture. The temperature of the liquid trap was evidently 

 too high to make chlorite from the constituents of the pyrox- 

 ene. Moreover, the feldspar is not much altered notwithstand- 

 ing the moisture at hand. 



This dike, from the underside of the West Rock trap-mass, 

 suggests an hypothesis with regard to the origin of the low 

 and narrow belt of amygdaloidal trap that runs parallel with 

 the high and wide belt of compact and nearly anhydrous trap 

 of the Mt. Tom Ridge, from western Meriden northward, 

 keeping in close parallelism with it and bending with it east- 

 ward at its southern extremity in the Meriden region. On 

 Percival's map, Plate XYI in vol. xlii, of this Journal, the 

 belt is that of the series of narrow dikes lettered A 1, situated 

 just west of the areas 3, 4, 5, 6, 7, 8, 9, which mark the main 

 trap range. It follows the curves and variations in height of 

 the main range. 



The hypothesis of Prof. ¥m, M. Davis supposes that this 

 low amygdaloidal belt is the outcrop of an inferior sheet of 



* Synthase des Mineraux et des Koches, 1882, p. 62. 



f This Journal, III, ix, 187. G. W. Hawes obtained for the composition of the 

 trap (doleryte) of West Hock (mean of two analyses): Silica 51-78, alumina 

 14 - 20, iron protoxide 8 - 25, iron sesquioxide 3'59, manganese protoxide - 44, 

 magnesia 7 - 63, lime 10 - 70, soda 2 - 14, potash - 39, phosphoric acid 0*14, ignition 

 0Q3=z9?rS9; and for that of its pyroxene: Silica 50 - 7l, alumina 3 - 55, iron pro- 

 toxide 15 - 30, manganese protoxide 0-81, magnesia 13 63, lime 13'35, ignition I'll. 

 [alkalies and loss, 1-48] = 100. 



