I 36 THE AMERICAN NATURALIST. (VoL. XXXIII. 
tion in the negative on page 363 of the article under review, and 
in the affirmative on page 369.!_ If an affirmative answer be not 
possible, there is no possible explanation of these higher crests 
in the light of our present geological knowledge. Monadnocks 
like the Blue Hills near Boston, Ascutney Mountain, Chocorua, 
Katahdin, are made of plutonic rocks, necessarily crystallizing 
under the pressure of overlying masses of the same lithological 
character as the rocks now seen in the immediate vicinity of 
these eruptive centers. The overlying rocks are gone, the sur- 
rounding rocks are well beveled down; the stock-rocks stand 
up as knobs — Why ? — because they are harder. If there can 
be suggested a simpler, more probable explanation, it is high 
time that geologists should find it out. 
It has been my fortune to map geologically one of these typi- 
cal monadnocks, Mount Ascutney, and, on all sides of it, to 
meet with striking illustrations of the fact that it stands above 
the general level solely because it is more resistant to destructive 
agents. The streams running across the syenites and granitite 
far up the mountain are slowly cutting their gorges, continued 
in radial arrangement, across the contacts on all sides. At the 
contacts there is almost universally an abrupt fall where the 
streams escape on to the thinly foliated schists or basic intru- 
sives that encircle the main mountain. This exhibition of 
differential hardness is correlated with an only less important 
steepening of slope where not the perennial streams, but the 
general process of wasting and wash, “creep,” has developed a 
sudden fall-off just at the zone of contact of intrusive and 
country-rock. In the reconnaissance of the mountain this lat- 
ter slope was used as a rapid means of locating the contact. 
Now “hese are the test cases. It is, indeed, difficult to say why 
the gneissoid and schistose rocks of Mount Monadnock have 
refused to weather down as rapidly as the similar schists round 
1 On page 363 we read: “I believe that I am correct in saying that there are no 
very distinct differences between the rocks of the monadnocks and the lower hills, 
in point of durability.” On pages 368 and 369 we have: “ There will be a bevel- 
ing of hilltops where the harder gneissic and granitic rock exists, the stream 
valleys standing near the base level, and hills of softer strata standing at levels 
still lower, in which on rock is semen ... Can any evidence be adduced to - 
show that New E g d further in devel han this stage?” 
