WARREN. — ALKALI-GRANITES AND PORPHYRIES. 305 



the erosion requisite to lay bare the bathoHth, and occupying in its 

 broader, dike-like development between the east side of Pine Hill and 

 the summit of Wampatuck Hill, a steep-walled valley due to the 

 erosion of a deeply included 1)ody of slate. Depressions having this 

 origin exist in the modern topography, the valley of Ruggles Creek 

 being a good example. If now, we conceive such an erosion trough, 

 with its wall of quartz-porphyry essentiallj^ intact, as the Ruggles 

 Creek Valley is today bordered by the contact zone of fine-granite, 

 to be traversed longitudinally by a fault fissure with a down-throw to 

 the south, as the valley of Ruggles Creek unquestionably is, the out- 

 flow of acid lava filling the depression and connecting fissure, and 

 flowing out away to the south, would seem to account for all the facts 

 as they are now developed in the field." 



Under the first view it seems to the writer very difficult to conceive 

 of a magma forcing its way in between the contact porphyry and its 

 slate cover in such a way as to carefully remove all of the slate over a 

 great area of what was certainly a most uneven contact svu'face with- 

 out leaving, so far as known, a single fragment of it between the por- 

 phyry and the aporhyolite.^^ Under the second view, it seems very 

 unlikely that erosion, accompanied by even the most favorably dis- 

 posed faulting, could have removed the slate cover just so far as the 

 fine-grained contact phase of the porphyry and no farther, for the 

 aporhyolite never comes in contact with any other phase of the liatho- 

 lithic rocks ; and this over a wide area, at various elevations and along 

 a most devious line of contact. Furthermore, it would seem almost 

 inevitable under either hypothesis that the lava would have included 

 within itself fragments of either the slate or the porphyry, or both, 

 and such inclusions are nowhere to be found, at least along the great 

 length of contacts which have been examined by the writer. The 

 porphyry at all of its exposed contacts with the aporhyolite bears 

 all the characteristics of a chilled contact phase against something, 

 and it appears most natural to assume that the chilling was done by 

 the rock with which it is now in contact — the aporhyolite. It is 

 wholly inconceivable that the aporhyolite itself, a rock, that in large 



63 It should be noted that the aporphyolite is in contact, according to Crosby, 

 with slate northwest of Fox Hill, but the precise relation of the slate to tfie 

 nearby granite and porphyries is unknown. The only other slate anywhere 

 near the aporhyolite is a fragment, 2 ft. across, embedded in the granite- 

 porphyry just east of the easternmost, and very narrow end, of the aporhyolite 

 in the Pine Hill area. 



