American Association. 26J. 



]aiid — iu the same way. i\.l"tei' quoting the published opinions of 

 Professor Hitchcock, Professor Dawson and others, Professor Cook 

 said — After examining all he had been able to find written, he 

 could find no other theory which would embrace all the facts, than 

 that of a slow and continued subsidence of the ground. In regard 

 to the rate at Avhich this subsidence was going on, the Professor 

 quoted the result of several examinations, and said with these se- 

 veral results — three of a subsidence of 3 feet in 150 years, one of 

 two feet in 100 years, two of 1 foot in fifty years, — and one of 4 

 inches and one of 8 inches in 2 years, he might, with some de- 

 gree of probability, set the average subsidence in the district 

 w-here the observations were made, at two feet in a century. The 

 opportunities for accurate observation was less frequent in several 

 of the places mentioned than in the southern part of ISTew England ; 

 but from the phenomena of the marshes and of the submerged 

 forests of Long Island and in northern New Jersey, he inferred 

 that there was no material diiference in the rate from that already 

 deduced. " 



METAMORPIIISM OP SEDIMENTAUY ROCKS. 



A subject of commanding importance in chemical geology, is 

 the METAMORPHiSM OF SEDIMENTARY ROCKS ; but hithcrto chcmists 

 have regarded it as a difiicult and uninviting field. We are glad 

 to find that Mr. Hunt, of the Canadian Survey, has been culti- 

 vating it with marked success. His paper on this subject was 

 replete with suggestive facts and inferences ; much more so than 

 can be gathered from the following somewhat meagre abstract. 



" The fact which forms the point of departure for the history of 

 the metamorphic rocks is this : — That the sedimentary strata com- 

 mon to different geological formations, may under certain condi- 

 tions, be converted into crystalline rocks. One of the most important 

 results of modern geological research has been to show that the 

 crystalline schists of various regions are stratigraphically identical 

 with unaltered sediments of Silurian, Devonian, and even of later 

 secondary age, although regarded as primitive rocks by the geolo- 

 gists of the last generation. Mr. Hunt observed that we have besides 

 those sedimentary rocks of mechanical origin, which are composed 

 of the ruins of felspathic and quartzose rocks, others of organic 

 origin, and finally deposits of limestone, dolomite, magnesite, car- 

 bonates and oxyd of iron, and manganese. These chemical deposits 

 are often mingled with those of mechanical origin. He contended 

 that a dry heat, producing fusion of the sediments, cannot be 



