Geology and Mineralogy. 395 



whether he continued the section until the grain appears uni- 

 form. From Klimmel's report for the New Jersey Geological 

 Survey, 1897, p. 62, w^e learn that at one of the points — Fort 

 Lee — the sheet is 950 feet thick, of which Queneau's section cov- 

 ered only about 100 feet. Of the grain, Kilmmel says that while 

 on the whole the trap is coarse-grained, near the contact it is 

 fine-grained or occasionally slightly glassy, but this rapidly in- 

 creases in size within a few^ feet of this shale, w^here coarsest 

 tin tabular crystals of feldspar occur, two or three-eighths of an 

 inch in diameter. The King's Point trap near Weehawken he 

 estimates from 700 to 875 feet thick, and again Queneau can only 

 cover the margin of varying grain (3449'='^, or 105 feet). 



From his plates and figures it appears that, so far as he meas- 

 ured, the feldspars still steadily and uniformly increase in size, 

 but the rate of increase of the King's Point augite drops deci- 

 dedly between 23 and 34 meters. Thus the breadth of the zone 

 of augite which was formed before the center cooled is not far 

 from ]00 feet, or about one-eighth of the total breadth. This 

 would imply that the consolidation of the augite took place un- 

 der conditions of temperature, etc., a little nearer those of the 

 initial magma than those of the country rock, and that the feld- 

 spar was earlier formed. We may also infer from his equations 

 of grain (as shown by investigations of mine as yet unpublished) 

 that there is a contact zone of noticeable thickness in which the 

 temperature was appreciably increased, and that while his data 

 are consistent with Kilmmel's observations, the grain of the 

 augite at the center is not more than S'^™, being probably about 

 3mm — ^ result which it would be interesting to verify. Had we 

 the thickness noted, and that of the contact zone if convenient, 

 and a section representing the central belt, we could have a check 

 on the theory, as well as on the accuracy of the observations ; 

 for the estimation of the grain is a difficult matter, and I doubt 

 if an accuracy of 10 per cent can be obtained, though the diver- 

 gence of Queneau's observations from his curves is no fair test, for 

 he has done himself injustice, since the curve of linear grain of a 

 great intrusive sheet with a contact zone, like the Palisades, ought 

 not theoretically to be a straight line, but is enclosed by three 

 straight lines as external tangents, which it will usually follow 

 very closely, having only short easement curves near the points 

 of tangency. 



Queneau's statement that the zone of varying grain will vary 

 inversely as the temperature of the country rock, is not mathe- 

 matically accurate, and is probably intended merely as a reword- 

 ing of what I say on page 111, that the hotter the country rock 

 the less pronounced will be the zone of finer grain. But I may 

 say that if we have the curve of grain located well enough to 

 determine the three tangents just mentioned, we may infer the ' 

 ratio of the temperatures of injection and consolidation, the 

 thickness of the intruded sheet and the breadth of the contact 

 zone appreciably affected, as well as a constant involving the 



