292 BULLETIN OF THE 



chusetts sandstones {e, 655) ; the only possible case of the kind was 

 found on the south side of Mount Tom, near a saw-mill on a stream, not 

 far from the main road three miles below Northampton (e, 656).* 



In Connecticut dikes are comparatively common. The first examples 

 recognized were described and figured by Hitchcock in 1823 {b, 56); 

 they are in East Haven, eight narrow dikes within four hundred feet. 

 (See figs. 2 and 44.) Chapin was the first to describe and figure some 

 of the numerous and irregular dikes about Wallingford in 1835 (fig. 10). 

 Percival refers to all of these, and adds many others ; but it seems that 

 he sometimes applied the word dilce to sheets, and therefore we cannot 

 say how many of his examples would come within our limitation. Pine 

 and Mill Rocks at New Haven (G) are the largest dikes observed in 

 the State. 



Mather gives one or two examples from the face of the Palisades 

 (279, 282, here copied, figs. 11, 12). 



Cook finds only two dikes in New Jersey ; one near Blackwcll's Mills, 

 on the east side of the Delaware and Raritan Canal ; the other in a road 

 cut beyond the Flemington copper mine ; but he thinks it probable 

 that many others lie hidden below surface drift (6, 204 ; a). He later 

 says there are many places where the trap can be seen catting across 

 the stratified rocks, as by Hook Mountain, Palisade range {c, 32). 



In Pennsylvania and beyond, dikes become more common. H. D- 

 Rogers figures two examples (here copied, figs. 21, 22), and on the State 

 map (1858) a number are represented within and without the sandstone 

 belt : of the latter, the most remarkable is the long dike discovered by 

 Henderson, which extends some eighteen miles, across the Juniata and 

 Susquehanna near their junction. Frazer describes the dikes in Lan- 

 caster and the adjoining counties as so numerous and so difficult to trace 

 that he was unable to represent them all on his map (c, 27) ; he says, 

 also, " The outflow of trap probably followed one or more of the planes 

 of cleavage, of which these rocks are full " {h, 325 ; his sections showing 

 dikes are cautiously drawn without contact lines : compare extract below, 

 under Intruded Sheets). 



W. B. Rogers mentions dikes cutting across the sandstones in Vir- 

 ginia (6, 82), and Heinrich writes that, " Penetrating the sedimentary 

 rocks, igneous rocks ai-e occasionally met with in the form of dikes " 

 (244, also 250, 263). ' 



* Since writing the above, Professor C. H. Hitchcock tells me that he has seen 

 one or two small vertical dikes cutting the sandstone in a quarry on the southwest 

 slope of Mount Holyoke about half a mile from the Conuectieut, — the only examples 

 of the kind known to him in the State. 



