Page:Popular Science Monthly Volume 37.djvu/212

200 that the expression, "has been regarded" as a bowlder, has been employed. The reason of this is, that a recent examination of this rock (in March, 1890) has led Prof. Crosby to the somewhat startling conclusion that it is not a bowlder, but "simply an angular and prominent remnant of a large granite vein, still undisturbed in its original position upon beds of gneiss; and that its chief geological interest is found in the fact that, notwithstanding its



exposed position, it has survived the disintegrating influence of the elements and successfully resisted the pressure of the great ice-sheet." Prof. Crosby also states that, "through the undercutting action of the frost, forming quite an extensive rock-shelter" (i. e., the cavity or recess on the lower or valley side), "is afforded an opportunity to observe the actual contact of the massive granite and the finely laminated micaceous gneiss" upon which the granite rests.

For one of very limited experience to dispute the conclusions of such a trained observer as Prof. Crosby would be presumptuous; and yet it would not seem unreasonable to ask that they should not be considered as entirely determinative without a further careful examination of the problem on the part of experts. The question as to whether the contact of the granite of the assumed bowlder and the underlying gneiss is one of situation or of composition is not an easy one for decision, without a very clear opportunity for examination. The fact that such a