Burbank.] 194 [April 19, 



lines; toward the northwest at an angle of about 65°, to the south- 

 east at an angle varying from about 70° to a nearly vertical position. 



The deposits are all of very limited extent, the largest appearing at 

 the surface, not more than 220 ft. in length, the width at the widest 

 part being about 60 ft., including the intervening bands of gneiss. 



The accompanying sketch of one of the largest quarries was made 

 from a survey with the Plane Table, by a friend, Mr. Nathaniel Hill 

 of Lowell, to whose kindly aid I am much indebted. 



This quarry is situated about a mile southwest from the village of 

 Chelmsford, near the Littleton road. It has been abandoned for 

 many years, and is partly filled with earth and rubbish so that very 

 little limestone is now accessible, if indeed it extends to any great 

 depth. In some places it can be seen that all the limestone has 

 been removed, exposing the gneiss at the bottom of the excavations. 



The folding of the strata, enclosing cavities which held the lime- 

 stone can here be plainly seen. 



In the sketch, PI. I, Fig. 1, the unbroken lines show the walls of 

 the cavities opening to the surface, from which the limestone has 

 been removed. The space enclosed by the dotted lines at (a) repre- 

 sents one of the cavities which is completely arched over by the 

 gneiss, forming a cavern about twenty feet in length. 



At (b) is a lateral cavity or pocket, connected with the larger cav- 

 ern by a small opening through a thin stratum of the gneiss. At the 

 opposite extremity of this part of the quarry, the gneiss of the walls 

 is also curved and folded over the limestone. 



At (c) a projecting mass of the gneiss partly enclosed a pocket of 

 limestone. 



At the excavations marked (i?) and (.F) the limestone apparently 

 extended to only a few feet in depth. The cavities in which it oc- 

 curs were evidently produced by the dislocation of a portion of the 

 gneiss of the central fold. This dislocation appears to be of a very 

 small extent vertically, the greatest depth to which the limestone ex- 

 tended being not more than ten or twelve feet from the surface. At 

 the extremity of the central excavation (E), at the point shown by 

 the dotted lines at (d), a small cavern from which the limestone has 

 been nearly all removed is completely covered by the folding of a 

 layer of the gneiss, which also forms a portion of the thin partition that 

 separates this small excavation from the larger one at (C). 



Professor W. H. Mies, (who has visited these quarries with me, and 

 whose careful observations will, I think, confirm my views,) pointed out 



