GREGORY.] 
RHYOLITES. 
107 
everywhere flanked by altered sedimentaries. The contact metamor- 
phism and the relative position of the surrounding rocks are evidence 
that here, as in Mapleton, we have a locally intruded mass. 
Dikes of aplite and granite-porphyry connected with the main mass 
are well exposed in the railroad cuts at the north base of the hilly dis- 
trict. Some are minute streaks; some are 40 to 50 feet wide. They 
are seldom straight and with even borders for any distance, but branch 
and fork, or even form a rude network. These dikes exhibit some 
interesting features which will be considered under another heading. 
This granite is a valuable resource for Aroostook County, and the 
quarry opened a few years ago at Ludlow is already furnishing consid- 
erable stone, especially for engineering purposes. 
JiSflSSI 
Fig. 2.— View of Haystack Mountain; looking northwest. 
RHYOLITES. 
HAYSTACK KIIYOLITE. 
There is a prominent ridge of land extending north and south through 
the center of Castle Hill Township from the Aroostook River to near 
the head of Squawpan Lake. The State road crosses it a little to the 
west of the Castle Hill Hotel, and the Haystack road crosses it at the 
Halfway House. This ridge is formed of extrusive volcanic material, 
the north end being formed of the andesites grouped about Castle Hill 
and the south end of the rhyolites which have Haystack as their center. 
This mountain is the most prominent topographic feature of the Presque 
Isle- Ashland area, in which it is unique as to form and position (see 
fig. 2). It rises abruptly from the general plain to a height of about 
