84 PrescoWs Sketch of the Geology and Mineralogy 



" AMYGDALOIDAL TRAP/** 



In Saugus, on the west side of the river, between Childs' mills 

 and Saugus factory, is a round isolated hill, from seventy five to 

 one hundred feet in height, in which occurs a rock of moderate 

 hardness, green color, and argillaceous odour when breathed on, 

 containing imbedded in its substance, innumerable white sphe- 

 roidal nodules of quartz, feldspar, and carbonate of lime, from 

 the size of a pin's head to that of a rifle bullet ; but few however 

 exceed the size of an ordinary pea. This is the vari&loid wacke 

 of Professor Hitchcock. 



About half a mile south by west of the former locality, occurs 

 another of the same rock, but the imbedded nodules are not so 

 numerous as in the former, and some portions of the rock in 

 both localities, are entirely destitute of these imbedded nodules, 

 At the latter locality are several bowlders, of a different variety 

 of the same rock, t)f a rich chocolate color. The parent bed 

 from whence they proceeded has not been discovered. The 

 imbedded nodules are similar to those in the green variety, and 

 of the same white color. In some portions of one of these 

 bowlders, however, the imbedded substance was of a greenish 

 color, and not so distinctly nodular. 



A little south of the first locality, (the round hill) and in the 

 vicinity of the last, occur numerous bowlders of a conglomerate 

 variety of this rock, consisting of fragments of rounded masses 

 of different varieties, some of which are of the amygdaloidal 

 variety, others not; some a darker, others a lighter green ; some 

 more, while others are less compact. Some portion of this con- 

 glomerate forms a beautiful breccia, and is probably of the 

 grey-wacke series. 



MAGNESIAN, SERPENTINE OR VERD D 'ANTIQUE MARBLE. 



A valuable and interesting bed of Magnesian Marble occurs 

 in Lynnfield, and a quarry has been opened near the centre of 

 the town. It is said to extend from three to five miles in a north 

 east and south west direction, but in no place, except at the 

 quarry, has it been found sufficiently soft to be worked with ease. 



* Varioloid wacke of Prof. Hitchcock, but Dr. Jackson considers it as Amygdaloidal Trap. 



