1880.] ANT [Benton. 
Coming down to 1870,! Dr. T. Sterry Hunt states in the Proceed- 
ings of this Society, that the amygdaloid of Brighton is a crys- 
talline, stratified rock. 
_ All these writers regarded the amyedaloid as a stratified rock, and 
three of them assert that it passes by a gradual transition into the 
Roxbury conglomerate, and consider it to be merely a variety o 
that rock. 
In a paper by Mr. W. W. Dodge,? published in the Proceedings of 
this Society in 1875, these rocks are treated as hornblendic. The 
writer had observed in various places their contact with the conglom- 
erate series, and therefore regarded them as being, at least in part, of 
eruptive origin. 
In January, 1879,8 Prof. N. S. Shaler read before this Society a 
paper in which he said: “It seems to me that these rocks afford 
evidences that the shales and conglomerates of the Roxbury series 
pass at certain points into an amygdaloidal trap which has been 
ejected through the overlying beds.” 
** With care and with favorable conditions of the quarries the 
observer may trace the stages of this transition from the faintest 
beginning of the amygdaloidal structure in rocks which are distinctly 
conglomerates, into rocks where the blebs (or amygdules) have been 
so completely developed, that every trace of the original pebbly 
structure is now lost and the mass converted into an amygdaloidal 
trap.” 
Thus all the writers on the amyedaloid with the exception of the 
Dr. Dana, Dr. Hunt and Mr. Dodge, maintain that there exists a 
gradual transition between that formation and the Roxbury conglom- 
erate. 
It is to be observed, however, that there is a radical difference 
between the cause assigned for the transition by the earlier writers 
and that assigned by Prof. Shaler; for the former merely considered 
the two rocks as of common origin, while the latter maintains that 
the one rock originated from the other; that is to say, that we have 
here an instance of the transformation of a sedimentary rock into an 
igneous one. 
1Proc. Bost. Soc. Nat. Hist., x1v, 45. 1870. 
2Proc. Boston Soc. Nat. Hist., xv1I, 416. 1875. 
3 Proc. Bost. Soc. Nat. Hist., xx, 129. 1879. 
PROOEEDINGS B. S. N. H.— VOL. XX. ati MAY, 1881. 
