MUSEUM OF COMPARATIVE ZOOLOGY. 173 



which place such an important fact beyond question will be described 

 in detail, so that other observers may obtain the evidence. 



Fortunately we need not depend for a knowledge of the relations of 

 the roclis in question upon a region in which the absence of exposures 

 along the line of contact renders it difficult to tell what may be true. 

 Upon the northern boundary of the stratified group, from Break-heart 

 Hill westward towards Main Street, the relations of the rocks are clearly 

 exposed. Between Break-heart Hill and Main Street several distinct 

 contacts of the felsite and quartzite may be seen, and there are no indi- 

 cations whatever of a transition between the two rocks. It will be 

 remembered that, in describing Break-heart Hill, it was mentioned that 

 the complex mixture of felsite and ashes extends from the summit down 

 the southeastern slope to the rocks of the stratified group. Near the 

 middle of the slope facing Mr. Edmond's house is a small ledge, furnish- 

 ing an excellent exposure in which the felsite, with contorted banding, 

 overlies unconformably at a large angle the upturned edges of the 

 stratified gi'oup. The rocks beneath are in part quartzite iuterstratified 

 with other rocks of the same group, and the line of contact sloping down 

 the hill is well marked. A short distance to the eastward the banding 

 in the felsite and the distribution of the ashy material has the same 

 general slope as the plane of contact. 



It seems to us that this very interesting exposure places beyond the 

 possibility of a doubt the conclusion that the felsite is younger than the 

 rocks upon which it reposes. A few rods to the southwest of the ex- 

 posure just noticed there is another, which shows apparently one side 

 of a dike of felsite cutting through the stratified rocks. The line of 

 contact is very distinctly marked and irregular, like that of an eruptive 

 rock, and is at right angles to the bedding of the adjoining rocks. 

 Distinct fragments of quartzite belonging to the stratified group are 

 enveloped by the felsite of this locality, and small ones have been found 

 embedded in the ashes. 



The facts observed upon Break-heart Hill are in harmony with the 

 relative positions of the two rocks as determined by the relations of both 

 to the granite, and there appears to be no doubt that the stratified rocks 

 of Melrose and the adjoining towns are older than either the granite or 

 felsite. 



Having considered the relations of the older rocks to the felsites, let 

 us turn our attention to the relations which the felsites hold to one 

 another. Mr. Crosby has shown that the rocks of the group vary widely 

 in chemical composition, and Dr. Wadsworth has called attention to 



