342 Lowell. — Geological Facts. 



At one place half a mile from the river, where the strata have been 

 denuded of the soil and diluvium, there are cut in the rock numerous 

 furrows, such as are usually called diluvial scratches; their direction 

 appears to be mainly N E and S W ; this rocky ledge is near to the 

 place where the rail road enters the town. 



But the most remarkable geological feature in Lowell remains to 

 be mentioned. The great rail road from Boston, just before its ter- 

 mination, passes through the solid rocks in a cut, which is a quar- 

 ter of a mile long, and in some parts it appears to be forty feet 

 deep. The rocks are mainly mica slate, the strata of which are in- 

 clined at very high angles of elevation, and in many places they are 

 nearly or quite perpendicular. Here are exhibited, on a great scale, 

 the most decisive proofs of the intrusion of rocks by force from be- 

 low. The intruding rocks are chiefly trap, varying in quality be- 

 tween greenstone and basalt, and sometimes inclining a little towards 

 the character of hornblende slate. It is evidently unstratified, but 

 still, from its having been forced in between layers of a stratified 

 rock, it has to a certain degree, copied the appearance, and in some 

 places has a little false show of stratification which, at a small distance 

 firom the principal rock, vanishes and it becomes massive and amor- 

 phous. 



The strata of mica slate, enormous as they are, appear to have 

 been heaved from their beds and raised from their horizontal po- 

 sition, by the same effort which injected among them the ignited 

 and melted trap. The latter has not here, as in many other situa^ 

 tions in various parts of the world, broken across the strata, and in- 

 truded itself between their jutting ends, thus dissevering the parts, 

 so as to form dykes or walls of trap bounded by the parted rock — 

 the trap has on the contrary, been here shot in between the strata 

 and has taken the direction of their beds, at the same time that the 

 vast heaving power which melted and threw up the trap, also raised 

 the enormous ledges of mica slate into their present elevated posi- 

 tion. 



The trap has therefore, in this case, been wedged in between the 

 strata, and has produced the following effects. •/ '' 



1. It has, in many instances, completely severed the strata of mica 

 slate, passing through between them often with undiminished thick- 

 ness, and appearing at their upper edges. 



These intruding walls are of various thickness fi'om a few inches 

 to a foot, to several feet or several yards ; the -thickest mass is eighty 



