125 



Eozoon canadense, together with the accompanying gneiss, 

 to the Laurentian system. The Eozoon has also been found 

 in the limestone in Bolton ; and there can be no doubt that the 

 range of limestone deposits extending through Bolton, Boxford, 

 Littleton, and Chelmsford, and coinciding in trend with the 

 strike of the enclosing gneiss, is of the same age throughout. 

 Now these limestones are rich in accessory minerals, and con- 

 tain the most of the species named by Dr. Hunt as occurring 

 in Montalban limestones. Taken collectively, these deposits 

 have afforded the following list of mimerals:^ scapolite, bol- 

 tonite, nuttalhte, chondrodite, petalite, sphene, pyroxene, 

 diopside, apatite, actinolite, asbestus, augite, allanite, coccolite, 

 pargasite, chromite, pyrite, magnesite, phlogopite, talc, ophite, 

 chrysotile, satin spar, rhomb, spar, spinel, and garnet. The 

 gneisses accompanying the limestone' appear to be indistinguish- 

 able from those forming a large part of the Montalban series 

 in Massachusetts, and, furthermore, they contain, or are 

 du-ectly in the strike of similar gneisses containing limited beds 

 or concretionary veins of coarse pegmatite rich in muscovite, 

 and holding tourmaline, garnet, beryl, and other minerals. On 

 stratigraphic grounds, also, we seem compelled to regard these 

 gneisses and included limestones as Montalban ; for, as Mr. 

 Burbank has shown, they form part of one and the same con- ' 

 tinuous and conformable series extending from Concord to the 

 Nashua Eiver, the other members of which, especially to- 

 wards the Avest, are unquestionably of this age. Then, 

 again, the occurrence of considerable deposits of steatite at 

 various points in this gneiss tells strongly against the view that 

 it is Laurentian, for this mineral is said never to occur in the 

 Laurentian formation. According to Hitchcock,^ a bed of 

 steatite, not less than fifty feet thick, is distinctly intercalated 

 with the gneiss in Andover. The steatite in Millbury and 



1 According to Mr. L. S. Burbauk, who has given much attention to the study 

 of the distribution, mode of occurrence, and mineral contents of the limestones in the 

 towns named. 



^ Final Report on the Qeol. of Mass., p. 157. 



