208 



not inclutled in the foregoing nieusuremcnts ot" the beds which 

 it intersects. Farther south on the line of Hersey Sti'eet the 

 sandphiin conc(nils everything for nearly 500 feet ; and the first 

 outcrops in that direction are granite and diorite, with other 

 larofe masses of diabase. 



Most of tlic l)eds which we have crossed on Hersey Street 

 can be traced east by satisfactory outcrops to Lafayette Avenue. 

 Tlie strike gradually changes in this direction, however, from 

 nearly due east-west to east-southeast, as the map shows. Of 

 tlie most northerly conglomerate (lo) there is only one small 

 and rather uncertain exposure neai'ly GOO feet from Hersey 

 Street. The first red slate (12), after a gap of 700 feet, is 

 well exposed behind Mr. Lane's house on South Street. It 

 forms an abrupt escarpmentor cliff from 15 to 20 feet high, and 

 has also been found in excavations 50 feet or more north of tiie 

 cliff. Tlie di[) at this point is only 25°, which fully accounts 

 for the increased breadth of the bed as shown on the mnp. 

 South of this slate we arc able to identify in almost continuous 

 ledges the folh»wing beds: conglomerate (11); red slate 

 (10), not clearly exposed, but represented by a blank depressed 

 space of the proper width; conglomerate (D) ; red slate (8) ; 

 conglomerate (7) ; red and gray slate (0) ; and gray sand- 

 stone and slate (5). The more southerly beds along this line 

 have apj)roximately the same dip as on Hersey Street — S. 

 70° ; but toward the nortli the dip diminishes to 50° and 25°. 



The first slate (12) and the first and second conglomerates 

 (11 and i)) are well exposed also in the angle east and south of 

 Lafsiyettc Avenue. The structure here is much more compli- 

 cated and interesting. Immediately in the angle of the avenue 

 the slate is in contact witli the conglomerate (11) as usual; 

 but 100 feet farther cast it rests in like manner against a 

 ])arall('l mass of granite ; while the conglomerate abuts squarely 

 a<iainst theuranitc and the "frcat dike of diabase from 50 to 70 

 feet wide which interrupts tlie granite at this point. The 

 cranite, which has a breadth of from 40 to 50 feet north of the 



