1871.1 191 [Burbank. 



These discoveries led me to undertake a more careful examination 

 of other limestone deposits included in the same formation ; and in 

 May, 1870, 1 devoted several days to a more thorough exploration of 

 some of the old limestone quarries, including the well known mineral 

 localities of Bolton and Boxboro'. 



These examinations resulted in the discovery of the eozoonal rock 

 at all the quarries visited ; though it appeared in the greatest abun- 

 dance at Bolton and Chelmsford. 



Specimens of the rock from Bolton and Boxboro' were carefully 

 examined by Mr. Bicknell of the Museum of Comp. Zoology ; and 

 the radiating and branching tubuli, like those of the Chelmsford 

 specimens, were clearly identified by him. 



The eozoonal rock was also found in place at several of the 

 quarries, and its position in relation to the other rocks observed. At 

 all the quarries that I have visited, the limestone has been so 

 thoroughly worked out that the limits of its extent at the surface can 

 be readily traced. So completely are some of the quarries exhausted 

 that it is now hardly possible to obtain specimens of the rock that 

 constituted the mass of the deposits. The relation of the limestone 

 to the enclosing rocks can thus be readily seen. 



By the careful study of these relations, as observed at the time 

 above referred to, and by reference to specimens collected and facts 

 observed during many previous visits to some of the quarries, the 

 conclusions have been reached which are here presented. 



1 . These limestones are not true stratified rocks laid down with the 

 gneiss, but are subsequent deposits of a vein-like character. The fact 

 that some of these deposits appear to be inter stratified with the 

 gneiss, and also are found along a line apparently coinciding with 

 the strike of the strata, may seem to indicate that they are parts of 

 original strata included in the gneiss ; but their position may also be 

 explained in accordance with another theory, in support of which I 

 shall offer some evidence. 



2. Hie principal deposits occur along the line of an anticlinal, fill- 

 ing cavities produced by the folding and the falling down of portions of 

 the included strata of the gneiss. The anticlinal position is most 

 clearly shown at Chelmsford, where there are four veins or masses of 

 the limestone, in two lines coinciding with the strike of the gneiss. 



These lines are about half a mile apart, extending in a N. E. and 

 S. W. direction; the strike, as observed by the compass, being N. 65° 

 E. The strata of the gneiss dip in opposite directions from these 



