368 The American Geologist. June, 1895 
of the four limbs of the vertebrata — from a supposed similar 
but horizontal membranous flap, does not at present rest on 
an equally secure basis. If it is true, then changes have oc- 
curred in these far more profound than any of which we have 
evidence in the former organs. But the greater amount of 
supposition required in the case of a lateral fin-fold is of 
course an obstacle not to be lightly estimated. And from this 
point of view it is therefore exceedingly interesting to find 
what ma}^ prove to be an ancient relic of such a primeval lat- 
eral fin in these Devonian sharks. If the archetypal fold ex- 
tended from the pectorals to the ventrals it may as well have 
extended further to the place of these post-ventrals, if we 
may so call them, and then have run into the caudal fin and 
so met and fused with the dorsal-ventral fold, encompassing 
the body horizontally as the other encompassed it vertically. 
It may be rank heterodoxy to even hint at the existence of 
a third pair of limbs in a vertebrate. But on the above view 
there is nothing monstrous or incompatible about it. It is 
anomalous judged from the existing creation, but so was the 
pineal eye thought to be when first mooted. Yet it is now an 
accepted fact in anatomy of which, however, few traces have 
survived to the present. Possibly further discoveries in Pale- 
ontology may bring to light other indications of the curious 
organs here described. Whether the solution above suggested 
be the true one or not, it is certain that some Devonian sharks 
possessed these singular appendages whose origin must in 
some way be accounted for. 
CAMPTONITE DIKES NEAR D AN BYBOROUGH, VT. 
By N'ernon F. Marsters, Indiana University, Blooniington, Ind. 
Some twenty-five miles south of Rutland, Vermont, on the 
Bennington & Rutland railroad, is situated the little village 
of Danbyborough. The town rests in a deep, narrow valley 
or gorge-like depression, drained b}^ an extension of the Otter 
creek or river. This stream runs north through Rutland, 
Pitsford and Middlebury and finally empties into lake 
Champlain at a point nearly due west of Ferrisburgh. On the 
west side of the valley, in the region of Danbyborough, the 
