266 



GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



most fossiliferous ; and the liue of outcrops is continued by more scattered 

 openings farther southwest. It extends in all about 407 feet from northeast 

 to southwest — that is, along the line of strike. It is for the most part a 

 coarsely crystalline, saccharoidal limestone, at times so coarse that cleavage 

 pieces of calcite 3 inches across can be obtained from it. Below, it is in 

 thick beds, with stratification mostly obliterated, while the upper portion 

 for about 6^ feet is thin-bedded, finer-grained, and micaceous. The rock 

 contains some pyrite, which, with the more abundant deposit of the same 

 in the bottom of the quartzite, has been the source of the great amount of 

 porous limonite which fills broad veins and great cavernous spaces in the 

 limestone. Its modern formation is attested by the rootlets, changed into 

 limonite, inclosed in it. 



f IG. 18. — Section at north end of limestone, Williams farm. The two lower outcrops of quartzite are separated from the 

 rest of the section by an east-west fanlt. 



To turn over a mass of coarsely crystalline marble and find the 

 weathered surface covered with crinoid stems or corals makes a strange 

 impression upon one. In masses showing no trace of fossils these are 

 brought out equally well in thin sections, and I have even observed a 

 fragment of the shell of a brachiopod preserving the punctate structure, the 

 pores agreeing closely in position and measurement with those of modern 

 genera. 



In the section, fig. 17, all the fossils known are assigned to then- 

 proper horizon, so far as possible. I would especially note the fact, to 

 which my attention was first called by Prof. J. M. Clarke, that the line of 

 division between the two paleontological horizons represented falls well 



