CAIJBOX iniHil"] AM) SI'UINC HILL (iUOUP. L^'.t 



Eiii])r;ice(l witliin tliese lines ot" faulting < ml \' ( 'arlxniitcrous l)e(ls are exposed, 

 nlicreas tlie iucldsiui^ outer walls on Ijotli sides eoiisist of Silurian rocks 

 traceable the entire leng'th oi' tlie mountains except where concealed hy 

 volcanic overflows. P^issures alon<>' these fault lines have served as conduits 

 for extravasated lavas, tliroUi^li wliicli lia\e jkhuhmI out, either U]»on one side 

 or tile other, vast accumulations of volcanic material, for nearly the entire 

 lenjith of the mountains. So extensive have been these flows over the 

 Carboniferous rocks that not onK' luiAe the fault planes become obscui'ed, 

 but large areas of the setlimentary beds lie concealed beneath the lavas, 

 while in the region of the lloosac Mountain tlusv have so spread out 

 over the countrv as to completely burv all the underlving rocks between 

 tlu^ two faults. Natui'ally such an amount of volcanic, energy displaved 

 all along the line has broken and dislocated the strata, caused minor fault- 

 ings and displacements, and over much of the area rendered it diHicult. if 

 not imp()ssil)le, to work out the structural relations of tlu^ exposed bed.s. 

 Man\- fractures and breaks in the inclosed rocks, although not of any great 

 magnitude, are frequentK' sutHcient to render any })r(!cise measurement of 

 the beds impo.ssilde, the amount of faulting being undeterminable. On 

 the other hand great blocks of strata have been tilted up at high angles 

 with onl\' sliglit disturl);nic('s, afl'ording fairh' good cross-sections. 



The volcanic rooks separate the sedimentary beds, whi(;h otherwise 

 would form a coutinmmsbodv, into two or more di.stinct areas, the northern 

 known as the S[)ring Hill grou]) and the southern as tlie Carlson Ridge, 

 while l)etween them lies a much smaller area of limestones evervAvhere sur- 

 rounded l)v eruptive rocks. The middle area serves in a measure to connect 

 the other two, the same beds found here occurring both noi-th and south. 

 Acro.ss the southern end of Spring Hill, where the strata are less dis- 

 turbed than elsewhere, the limestones j)resent a synclinal fold whose axis 

 lies on the west side of the ridge east of Spring Hill. Adjoining tiie 

 Hoosac fault lies a low, narrow ridge separated from the main bodv of lime- 

 stone by a north and south fault, beyond which the limestones on S])ring 

 Hill dip casterlv at an angh^ of ,'{0°, the beds on the oj)posite side of 

 the fold attaining angles as high as M° westerlv. .Measured on the line 

 of the main section there are about 3,400 feet of limestones included 



