EASTERN MASSACHUSETTS. 



405 



nite. The clay slate was thought to underlie all the other i-ocks to form 

 the islands in Boston Harbor. The presence of slate in Quincj was 

 loticcd. The rock of Marblehead was designated as syenite. The 

 Maiden felsite was called porphyry, and that of Saugus a "bright red 

 jasper." Of JN^ahant he remarks that the slate " has undergone a strik- 

 ing change from the presence of the huge veins of trap with which 

 it is traversed in every direction." Prof. Webster previously had pub- 

 lished a short account of the limestone of Stoneham, which he thought 

 was probably in a bed. (Bost. Jour. Phil, and Arts, 1823-24, L, pp. 

 95, 96.) 



In the Keport on the Geology, Mineralogy, Botany, and Zoology of 

 Massachusetts, by Prof. Edward Hitchcock, published in 1833, consider- 

 able attention was given to the geology of Eastern Massachusetts. (See 

 also Am. Jour. Sci., 1833, (1) XXII., pp. 1-70.) 



The conglomerate of Brighton and elsewhere was denominated gray- 

 wacko, said to be stratified, and "sometimes beautifully amygdaloidal." 

 The amygdaloidal portion was regarded as " rather wacke than gray- 

 wacko." The wacke "often forms the cement of gray wacke." The 

 localities of the amygdaloid were given as Brighton, Brooklinc, JSTewton, 

 Needham, Hingham, and Saugus. (/. c, pp. 33, 34.) It can be read- 

 ily seen from reading President Hitchcock's report that beholds that all 

 the amygdaloidal melaphyr above mentioned passes into the conglom- 

 erate, the former being only a variety of tlic latter. The amygdulos 



t 



were according to him formed by fusion, except in some cases where 

 they were formed by infiltration. {I. c, pp. 248~2G2.) The argillite of 

 Nahant he regards as part of the graywacke formation belonging to the 

 Transition. The argillite there he calls flinty slate, and appears to hold 

 that the induration was caused by the trap veins passing through it. 

 He also remarks : — 



"The aluty structure is rurely lost, except at the junction of the greenstone 

 and nlate, where the two rocks are so intimately blended, that it is not easy to 

 fix upon the spot where either of them commences. This corresponds with 

 the opinion of. Dr. Maculloch, that nothing but the requisite degree of heat ii. 

 necessar}'^ to convert argillaceous slate into greenstone." {I. c, p. 265.) 



The argillite (argillaceous slate of Hitchcock) in the vicinity of Boston 

 was described with the graywacke formation, although President llitch- 

 cock was inclined to make it oldei. 



^ 



The limestone of Stoneham, Newbury, and Chelmsford, he held to be 

 in beds, modified by the action of granite and syenite, which had obht- 

 erated the lines of stratification. (I. c, pp. 308-313.) 



