1869.] ' 173 [Shaler. 



satisfactorily; being nearly destitute of fossils, and extremely compli- 

 cated by disturbances, they have not presented a very inviting field 

 for research. They have consequently received, as yet, very little 

 attention. I venture to offer here a few suggestions concerning their 

 relations, which may serve as a basis for future communications, and 

 for the study of those who may have the desire to examine the same 

 field. 



There can be no doubt that the syenites, which make up so large a 

 part of the exposed rocks of Eastern Massachusetts, are the oldest 

 materials found in this region. The best exhibition of them, showing 

 at once their general character and their relation to the superincum- 

 bent beds, is found in the immediate vicinity of Quincy, Mass. The 

 extensive quarries of that neighborhood enable us to see very well all 

 the different conditions of occurrence of this rock. The most re- 

 markable fact which has come under my observation is the exist- 

 ence of planes of separation in this syenite, which cannot be referred 

 to joints. The three or more planes of joint cleavings observable in 

 these beds are clearly separable from this other set of planes which 

 I cannot refer to any other cause than stratification, despite the 

 opinion still generally entertained, that these rocks are of igneous 

 origin, and owe their present structure to the actions which go on in 

 a mass in a condition of igneous fluidity. 1 That I am not mistaken in 

 referring these fractures to bedding, is, I believe, abundantly proven 

 by the details of structure of the syenite itself, as well as by the re- 

 lations it bears to the unquestionably stratified rocks which rest upon 

 it. These planes in question show none of the characters which are 

 presented by the true joint planes and fault's planes. There are no 

 slickensides. They are only imperfectly parallel, and of very varying 

 thickness. There are visible on the surfaee of considerable sheets of 

 this rock, laid bare in the Mitchell quarry near Quincy, splitting 

 along what I believe to be the plane of stratification, markings in- 

 distinguishable in appearance from ripple marks. This observation 

 was made upon quite a small surface, so that it alone could hardly be 

 trusted to determine the nature of these rocks. But upon the sides 

 and the summit of the syenite, at various points, we find other evi- 



iThe admirable researches of Dr. T. SterryHunt into the constitution and origin 

 of granite and syenites, have made it possible for the student to approach the 

 question of the origin of rocks of these groups with a better chance of ascer- 

 taining the truth than would have been possible before the publication of the 

 results obtained by them. 



