412 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



angle of about 45°. Dr. C. T. Jackson, later, gave the dip as to tlie 

 north, at an angle of 50°, (Proc. Best. Soc. Nat. Hist., 185G, VI., 



pp. 42-44.) 



The nextyear, Mr. Isaac Lea, however, on exarainhig the position of 

 the fossils in the rocks, concluded that the dip was to the south, and to 

 the amount of QS"". (Proc. Phil. Acad. Nat. Sci., 1857, IX., p. 205.) 

 This latter appears, beyond doubt, to have been a correct statement of 

 the direction of the dip, if not of its amount. 



Dr. Hunt, in 18G6, in his paper on the Laurentian Limestones, re- 

 marks of the crystalline limestones of Bolton and the adjoining towns in 

 Eastern Massachusetts, that they 



" rescmLIc iu geognostic and niineralogical characters, those of the Laurentian 

 system. There are however not wanting reasons for snppoaing them to be- 

 long to a more recent geologic period, and the facts recently observed in 

 Bavaria .... show, what was antecedently probable, that similar niinera- 

 logical characteristics may be found in crystalline limestones of very different 



ages. 



jj 



(Geol. of Canada, 1803-66, p. 197.) 



This was reprinted without change in 1871, in the revised edition 

 published in the Report of the Eegcnts for New York. (See also Am. 

 Jour. Sci., 1854, (2) XVIIL, p. 200.) 



In 18G2, Mr. T. T. Bouve claimed that he had traced, especially in 

 Hiugham, the passage of the conglomerate into a compact, homogeneous, 

 almost jaspery rock. (Proc. Best. Soc. Nut. Hist,, 1859, VIL, p. 183; 



18G2, VIIL, p. 57.) 



In 186 7 Prof Chas. H. Hitchcock remarked that there was reason to 

 believe that the gneiss and hornblende schist of Andover belonged to 



" Eozoic ages, perhaps as old as the Laurentian The evidence consists 



chiefly in the fact that pebbles of the syenite, which is newer than the schist, 

 occur in the Paradoxides slates near Boston, along with rod jasper, green por- 

 phyry, and other rocks associated with, the syenite. Tliese slates form the low- 

 est member of the Paleozoic series ; hence the rocks from which the peljbles 

 were derived are older than the Silurian, and must be Eozoic. Lithologically 

 they resemble the Laurentian gneiss and syenite, in the typical localities." 

 (Proc. Essex Institute, 1867, V., pp. 157-160.) 



Professor Hitchcock probably had in mind the argillites and conglomer- 

 ates, of whose ago nothing definite is known, for in the Braintree argillito 

 containing fossils, so far as the published records show, no such pebbles 

 have been found by the numerous observers who have examined it,* 



* Dr. Wadswortli has repeatedly examined the Braintree locahty with a like nega- 

 tive result, so far as the occurrence of pebbles is concerned. 



