354 C. L. Whittle — Main Axis of the Green Mountains. 



and more laminated, — and duplication of beds is very evident. 

 One often meets the same infolded limestone bed three times 

 on the steep western slopes of the mountains. The topography is 

 seen to be genetically dependant upon the enforced schistosity 

 while the stratigraphy exercises but little controlling influence. 

 Steep westerly slopes, however, are in part due to the less re- 

 sistant limestones in the troughs which, as on Pico undermine 

 the more resistent rocks and give rise to pronounced escarp- 

 ments. On a large scale Green Mountain folding is a parallel 

 of the minute plications so often observed in the crenulated 

 schists ; a vertical line would often penetrate the same bed 

 several times. As a result of sharp over-turning, thrusts prob- 

 ably occur but where metamorphism is so great it is doubtful 

 if they can be detected in many cases. 



A measure of the stretching and consequent thinning of 

 the strata on the backs of folds is frequently found in the 

 effect produced on pebbles in the quartzite or upon second- 

 arily-developed tourmalines. Pebbles of feldspar having an 

 original diameter of a quarter of an inch are now found 

 drawn out to four inches ; crystals of tourmaline which one 

 may fairly assume were not more than one inch in diameter 

 are now seen as linear films over a foot in length. Stretchino- 

 of so pronounced a character as this takes place commonly 

 along zones ; belts of slipping in quartzite are frequently met 

 where the surfaces for several hundred feet are ridged in 

 parallel lines as though the quartzite were pulled out in 

 the same manner that the confectioner stretches some varieties 

 of confectionery when partly chilled. Compensation is not 

 always made in this way ; in some localities minute faulting 

 takes its place. It is noticed that in the lower rocks the strain 

 is often relieved in this manner. Lower coarse gneisses, for 

 example, have not infrequently hundreds of minute faults to 

 the square foot ; along each of these fault planes, films of 

 sericite are developed giving the weathered rock a reticulated 

 appearance. Such faulting might suggest normal brecciation, 

 but there is only slight displacement not attended by crushing and 

 consequent destruction of the angularity of the faulted areas. 

 Zones of this character were probably too far below the sur- 

 face to be caught in the more superficial belt of crinkling and 

 stretching, but underwent great pressure under enormous load 

 giving rise to the observed faults, or the rocks suffered the 

 faulting before the border rocks were deposited. The last 

 explanation is regarded as much the most probable. 



The structure of the main axis of the Green Mountains is 

 thus seen to be a series of sharp, compressed folds striking 

 approximately north and south and overturned to the west in 

 most localities so that induced schistosity and stratification dip 



