!• PAL5:0NT0L0GY OF NEW-YORK. 



•with certain shaly beds in the Potsdam sandstone, or even perhaps at the 

 base of this formation*. 



* The rediscovery or this trilobito in an authentic locality, after a lapse of so many years, is extremely 

 interesting. The Paradoxidti harlani was described by Dr. Green in the Supplement to his Monograph 

 in 1835, from a specimen belonging to the Cabinet of Fkancis Aloeb. esquire, and believed to be from 

 an undoubted American locality. Since no other specimens have been seen, some doubt had arisen as to 

 the American origin of the one in question; and since the original has been lost, no other representations 

 of it remained except the cast of Prof. Gbeen. The specimens now obtained from Braintree are imbedded 

 in a rock of precisely the character of the original specimen obtained from Mr. Aluek, which the writer 

 well remembers seeing in the possession of Dr. Green. 



Onring this interval, fragments of trilobites have been several times foimd upon George's island in 

 Massachusetts bay, but they do not appear to have attracted the attention of the naturalists of the vicinity. 



The history of the present discovery appears to have been as follows : 



" About five years ago, Mr. Eliphas Hatward first observed these fossils on opening his stone quarry 

 for the purpose of obtaining underpinning and ballast stones. Without knowing their nature, he still looked 

 upon them as interestmg curiosities, and laid aside the specimens which have lately been brought before 

 this Society. 



" lie showed them to Peter 'WAixwBianT, esquire, of Boston ( Mass.), who at once recognized them 

 •a trilobites, and brought them to Boston for the inspection of geologists, and presented two specimens 

 to our associate Prof. William B. Rogers, to whom the Society is indebted for the first notice of these 

 remarkable fossils, so important in the determination of our geognostic horizon. 



" A few days after Prof. Rooebs's visit to the quarry. Dr. Jackson, by invitation of Mr. Wajnwbioht, 

 Tisited it and made a minute examination of all the geological phenomena which it presents, and obtained 

 specimens of the trilobites through the kindness of Mr. Hatward, and by search at the quarry in company 

 with Mr. Waimwbioht. Two specimens were obtained; one entire, which is 8^ inches long and 4 inches 

 wide. The other, of which only the head and half the body was obtained, is 6 inches wide, and its hood is 

 71 inches across by the base of the head : hence the length of this specimen must have been 12i inches at 

 least, which is about the size of the largest specimens of the Paradoxidet tetsini discovered in Sweden. 

 The smaller individual has 21 articulations, but none in the tail beyond the lateral ai)pendages, and in this 

 respect differs from the P. tetiini, its nearest analogue, which has, according to Brongkiart, four faintly 

 marked depressions or folds crossing the tail transversely. They may have been obliterated in our specimen 

 by the changes the rock has undergone. 



" These trilobites of Braintree occur in a blue gray argillaceous slate, containing silicate of lime, but no 

 carbonate, and some disseminated iron pyrites. Tlie stratification of the rock, as indicated by its grain and 

 cleavages, dips to the north 50 degrees, and runs east and west. It is but slightly altered by heat in those 

 portions where the trilobites are found; but near the sicnitc rocks, it is filled with nodules of epidote, and 

 closely resembles the altered slates of Nahant. There is a small vein of quartz, bearing iron pyrites in it, 

 which cuts through the slate strata at right angles. There are also slickensides surfaces on some of the 

 cleavages or joints in the quarry; indicating, as it is supposed, the polishing effects of rapid earthquake 

 movements at the period of disturbance of the strata at the time of their disruption by intruded sicnite. 



" Tliese are all the marks discoverable of metamorphic action of igneous rocks on these sedimentary 

 strata, though the slate rocks are hemmed in by the sicnite rocks on both sides, and the belt of slate is 

 quite narrow'." 



A notice of this discovery has likewise been pnblishcd in the American Journal of Science and Arts for 

 September 1850, by Prof. W. B. Rogers, who also read a notice of the same before the American Associa- 

 tion for the Advancement of Science. 



* Eztiaet from a Report mads to th« Boston Society of Natural History by T)r. C. T. Jackson. 



