58 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the melaphyr has been forced into the sediment. Fragments of the 

 latter have been torn off and lie embedded in the melaphyr. In places 

 the igneous rock breaks across the bedding planes, occasionally develop- 

 ing a contact zone, within which the bedding is obliterated and the 

 sediment hardened. 



The third " flow " is marked by a very irregular ridge of melaphyr, 

 extending, with a few interruptions, from Commonwealth Avenue across 

 Allston Street to Cambridge Street. Contacts with the slate are shown 

 in several places. The lower or southerly contacts need not be dis- 

 cussed. Whatever the relations of the melaphyr may be, those contacts 

 would necessarily be igneous. Contacts on the northern or upper side 

 are to be seen at the so-called carriage-house quarry on Allston Street 

 (Plate 2, Loc. 15), on the edge of the woods, two hundred yards north 

 of the elbow in Commonwealth Avenue, and in several exposures along 

 the northern face of the ridge at the end of Allston Heights (Plate 2, 

 Loc. 16). 



The slate at the carriage-house quarry (Plate 2, Loc. 10) is seen 

 lying on the back of the melaphyr ridge. It is tilted at a high angle, 

 dipping north 40°-60°. It is warped as though powerfully twisted. 

 The melaphyr just below the contact is full of slate fragments which are 

 twisted and gnarled as though they had writhed under the influence of 

 the molten mass. The actual contact is irregular. Tongues of the 

 melaphyr penetrate the slate, cutting the bedding, while the contact 

 zone is marked by a deep red band, varying from a sixteenth to a quar- 

 ter of an inch in thickness. Under the microscope the slate is seen 

 (Plate 1, Figure 1) to be penetrated by numberless tongues of the mela- 

 phyr, the bedding is cut and twisted, and little molten particles of the 

 slate fill the mass of the igneous rock. The feldspar crystals are fre- 

 quently aligned along the contact. Often the amygdules are seen 

 clinging to the little blebby fragments of slate, suggesting that the 

 latter may have influenced their formation. The plane of contact 

 does not lie exactly in the bedding planes, but cuts them at a slight 

 angle. 



The ledges on Allston Heights show the same phenomena. The 

 megascopic evidence is here even more striking. The slate is thoroughly 

 filled with fine tongues of the igneous rock. Frequently the two rocks 

 are mixed to such an extent that it is hard to say where the actual con- 

 tact is. In places the slate is baked to a hornstone, blotchy with red 

 and white, suggesting bedding lines which have become obscured in a 

 pasty rock. Here, again, the microscopic evidence is clear (Plate 1, 



