168 Distribution of the North American Flora. [ March, 
plicated topography of the ridges and river basins which it 
clothes. 
But by far the most remarkable fact hitherto reported regarding 
the disposition of the groves is, that they occupy only those 
spots in the Sierra which were first laid bare when its icy mantle 
became broken up into isolated glaciers. Thus, commencing at 
the north, the gap of forty miles between the Calaveras and 
Tuolomne groves was occupied by the great glacier of the Tuo- 
lomne and Stanislaus rivers; that between the Merced and Mari- 
posa groves by the glacier of the Merced river, which sculptured 
the famous Yosemite valley ; and so on—each’ successive group 
of trees occupying a lofty spur between the sites of ancient 
glaciers, and the greatest continuous extension of the forest (of 
forty miles) occurring exactly where, owing to the topographical 
peculiarities of the region, the ground was most perfectly pro- 
tected from great fields of ice. 
Mr. Muir, a very intelligent and accurate observer, who has 
studied the groves throughout their length and breadth most 
diligently, and to whom I am indebted for the above and much 
other information regarding the southern forest of Big-trees, con- 
siders that these have never since the Glacial epoch been more 
widely distributed or in greater vigor than now, and doubts, 
indeed, if the forests have reached their prime, founding his 
opinion on the high state of health of the mass of the trees, the 
multitude of seedlings and saplings in the southern groves, and 
the absence of any trace of trees having existed outside the 
present limits of the groves (as of dead trees, stumps, or the great 
holes left by fallen trees). 
Size of the Big Trees.—So little that is trustworthy has hitherto 
been published regarding the age, size and durability of the Big- 
tree trunks when fallen, that I shall offer you some accurate data 
which I obtained on these points chiefly from Mr. Muir. A tree 
felled in 1875 had no appearance of age, it was 69 feet in girth inside 
the bark, and the number of annual rings counted by three persons 
varied between 2125 and 2139. Another was 107 feet in girth 
inside the bark at four feet from the ground; its wood was very 
compact, and showed, throughout a considerable portion of the 
1 «Qn the Post-Glacial History of Seguota gigantea,” by John Muir, of San Fran- 
cisco, Cal, Proceedings of the Amer. Assoc. for the Advancement of Science, Buf- 
falo meeting, Aug., 1876. ee s 
