326 ' 77j(? American Geologist. May. 1901. 
their structural relatious. Apparently, every irregular or 
transverse contact is to be regarded as igneous, ignoring all 
the raggedness of a normal lava flow, to say nothing of subse- 
quent faulting and crushing, and ignoring the almost inevitable 
induration by silicification, of a sediment in contact with such 
a prolific source of free silica as these basic lavas were dur- 
ing the process of chloritization ; and certainly nothing is more 
normal than the impregnation of sediments in contact with a 
basic eruptive by ferruginous minerals, thus readily explaining 
directly or by subsequent oxidation the very local reddening of 
the sediments, extending commonly less than an inch from the 
contact, to which Mr. Burr attaches much importance. Of the 
excess of free silica during the alteration of the melaphyr we 
have substantial evidence in the quartz and jasper amygdules 
and segregations which often crowd the melaphyr and the nu- 
merous veinlets of quartz frequently to be observed in the im- 
mediately bordering sediments. 
Mr. Burr then discusses the structure of the region, to show 
that the melaphyrs are not confined to a particular horizon or 
limited part of the sedimentary series and that they are not 
continuous at any horizon. These contentions must be conced- 
ed, and so far as I know have never been questioned ; but they 
are certainly, to say the least, very inconclusive as arguments 
against the contemporaneous origin of the melaphyrs ; for there 
is no apparent reason why the volcanic activity should have 
been sharply localized in time, and certainly aerial continuitv is 
no more essential to efTusives than to intrusives. 
The account of the structure of this area on pages 61 to 66 
fails to indicate that the main features had been previously de- 
scribed. Reference may be made especially to the detailed ac- 
count of the thrust fault between the slate and the northern 
conglomerate. This is fully described and figured in my Con- 
tributions to the Geology of Eastern Massachusetts, published 
in 1880. I described it again, and with additional emphasis 
upon its structural importance in 1884 (Proc. Bost. Soc. Xat. 
Hist., 23, 24-27) ; and still again in 1889, in my lectures on the 
Physical History of the Boston Basin. 
So much it has seemed necessary to write in the interest of 
truth ; but it is only fair to add that the impetuous following 
of a narrow line of argument to its logical conclusion, regard- 
less of obvious and important counter arguments, which Mr. 
Burr's paper illustrates, is the more surprising since the author 
has previously done most excellent geological work ; and the 
explanation is undoubtedly to be found in a hasty study, under 
unfavorable conditions by a mind of more than ordinary ener- 
gy, directness and influence. As an example of Mr. Burr's 
lietter work, and as an indication of what may be hoped from 
him in the future. T may mention his brilliant paper of a vear 
