COLUMNAR TRAP IN THE UNITED STATES. 



149 



while the Cleveland basalt dyke passes through many of the upper 

 secondary strata, above the magnesian limestone, and is therefore of 

 posterior formation to that rock. 



Among the localities of columnar basalt given in a preceding part 

 of the present chapter, I omitted to state that there are very exten- 

 sive ranges of columnar trap in some of the northern United States 

 in America. Professor Silliman, in the seventeenth volume of the 

 American Journal of Science, has given a very clear description of 

 the basaltic range which divides the states of Connecticut and Mas- 

 sachusetts, extending one hundred and twenty miles in length, and 

 from three to twenty miles in breadth. It was believed a few years 

 since in England, that there were no basaltic rocks in the United 

 States. Messrs. C. T. Jackson and Francis Alger of Boston in 

 New England have recently published "Remarks on the Mineralogy 

 and Geology of Nova Scotia," with coloured plates, representing the 

 immense ranges of basaltic rocks on the shores of that peninsula. 



