414 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



dense had been found in the serpentine (Umestone) quarry at " Devil's 

 Den," Newbury. Prof. Hyatt then remarked that " the rocks of this 

 county [Essex] had been hypothetically refeiTed to the lowest known 

 series of Laurent ian strata " ; but that this was the first instance " in 

 which any positive evidence has been produced of their actual age." 

 (Bull. Essex Institute, 1869, I. pp. 141, 142 ; American Nat., 1869, 

 III., pp. 498, 499.) 



In 1869, Prof N. S. Shaler remarked : — 



" 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 most remarkable fact which has come luider ray ob- 

 servation la the existence of planes of separation in this syenite, which canuot 

 be referred to joints That I am not mistaken in referring these frac- 

 tures to bedding, is, I believe, abundantly proven by the details of structure of 

 the syenite itself, as well as by the relations it bears to the unquestionably 



stratified rocks which rest upon it There are visible on the surfxce 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 indis- 

 tinguishable from ripple marks If these syenites were of igneous origin, 



if they had been poured out before the deposition of the adjacent stratified 

 beds, or thrust through them in a state of fusion, we should expect to find the 

 usual marks of such actions. In the first of these cases the later sedimentary 

 deposits would be found lying unconformably upon the syenite without any 

 indication of transition ; in the second we should expect to find a clear line of 

 contact between the syenite and the sedimentary rocks, such as is always to be 

 found where an intrusive mass of trappean matter cuts more ancient rocks. 

 What we do find is that the imperfect bedding of the deeper portions of the 

 syenite becomes more and more clearly defined as we pass towards the exterior 

 of the mass, and gradually passes into unquestionably sedimentary rock. 

 Every stage of this transition is not clearly seen, but enough is visible to satisfy 

 any one that it really exists. The first rocks of quite unquestionable stratified 

 origin, lie directly to the north of the Quincy syenite hills, and consist of 



clearly bedded sandstones, approaching quartzites in their character 



Their general dip is northerly, with a variable angle of inclination which may 



be roughly averaged at twenty degrees Running the same north course 



across the break, we come upon the lowest of the Braintree series Its 



dip corresponds with the general inclination observable in the sup])osed strati- 

 fication of the syenite, as well as that of the quartzites immediately aliove it. 

 The whole of this Braintree series is fossiliferous, .... and although much 

 changed by metamorphic action, it is easily perceived that the whole set of 

 beds contains no trace of shore deposits. Immediately beyond the exposure of 

 the Braintree beds at Hayward's Landing, a dislocation has brought the thin 

 bedded quartzites again to the surface. The alteration in these is so great that 



