MUSEUM OF COMPARATIVE ZOOLOGY. 



285 



The following review, arranged by localities, beginning in the noi-th- 

 east, will give an idea of the various opinions that have been held. 



In 1833, Jackson and Alger (6, 276) described the Nova Scotia trap 

 along the Bay of Fundy as "an immense dike, thrown up from beneath 

 the sandstone through some vast and continuous rent, produced by the 

 sudden eruptive upheaving of its strata, which allowed it to spread out 

 laterally only to a very limited extent." In 1846, Gesner included the 

 same traps under the heading " Intrusive Igneous Eocks." 



In 1848, Principal Dawson in describing these sheets said (58) that 

 volcanic action ''brought to thQ surface great quantities of melted rock, 

 without disturbing or altering the soft arenaceous beds through which 

 it has been poured, and whose surface it has overflowed." This is quoted 



in his Acadian Geology, 1868. 



Bailey and Matthew mention stratified columnar and vesicular traps 

 and trap conglomerates on Grand Manan ; but further speak of the 

 traps as intrusive (219, 220). 



For Massachusetts, Hitchcock's first section (1818) shows the trap as 

 a vertical dike breaking across the sandstones; this was soon changed 

 (1823) and the trap and sandstone were described as in alternate beds 

 (6, 48), separating the old red sandstone on the west from the coal for- 

 mation on the east. In 1833, he described the conglomerate on the 

 back of Mounts Tom and Holyoke, consisting of "angular and rounded 

 masses of trap and sandstone, with a cement of the same materials," 

 and concluded that some of the trap must have occurred as a con- 

 temporaneous overflow {d, 211). In 1844, the same conglomerate is 

 ascribed to small precursory outbursts during the formation of the sand- 

 stone ; but the larger ridges are considered intrusive and of later date. 

 In 1858, he decides that all the Massachusetts trap is of overflow origin, 

 as will be referred to below. 



Lyell was shown the trap conglomerate on the back of Mount Tom 

 by Hitchcock, and inferred " that there were eruptions of trap, accom- 

 panied by upheaval and partial denudation, during the deposition of the 

 red sandstone" (a, 794). Leconte and Walling both adopt Hitchcock's 

 final view, and it is recently confirmed by Emerson. 



The rocks in Connecticut have given rise to other opinions. The 

 elder Silliman held that the trap was eruptive, but did not reach the 

 surface (1810-1830) ; his observations were mostly made when it was 

 still discussed whether the trap might not be of aqueous origin. Cooper 

 took strong ground in favor of the igneous origin of the trap, but did 

 not concern himself with the manner of its eruption : he implies, how- 





