PLAN OF THE SECTIONS AS A WHOLE 257 



ing Paleozoic times farther above the present surface than elsewhere in 

 the State. In the central part of the Narragansett basin, in the axial 

 center of the Taunton S3'ncline, the structure indicates a maximum depth, 

 of about two miles of sediments, measured to the floor of the Carbon- 

 iferous sediments — involving a deleveling and deformation of the Missis- 

 sippian land surface which took place during Pennsylvanian time, and 

 the later episode of Appalachian folding. On the west in the Taconic 

 Eange, where the time of folding is not yet clearly determined, the Pre- 

 cambrian surface is probably not at so low a depth below present sealevel. 

 The cross-section of the formations from the Hudson, on the west, to 

 Cape Cod, on the east, shows (1) on the extreme west the well known 

 Appalachian geosyncline of Cambrian to Devonian time; (2) a central 

 tract relatively stable during Paleozoic time and with a minimum of 

 compression and folding, made up of schists that are either of Carbon- 

 iferous or Precambrian age; and (3) an eastern segment. The last 

 named consists of folded patches of Cambrian strata intruded by grano- 

 diorites about Boston, and of Devonian at Danvers, Massachusetts. The 

 whole segment was probably mountain-built in mid-Devonian time and 

 intruded by granitic batholiths, followed by erosion to a low relief. At 

 the beginning of Alleghenian time crustal movement and igneous erup- 

 tions set in and the area became the seat of a very thick series of fresh- 

 water conglomerates and tillite (eastern part of Boston area), and finally 

 the entire segment was involved in the Appalachian folding and over- 

 thrusting movements about the close of the Paleozoic. The existing* 

 basins of conglomeratic sediments indicate the breaking up of a land sur- 

 face at the close of the Mississippian, accompanied by vulcanism and the 

 uplift of adjoining areas of erosion outside of the existing basins of 

 deposition. The increased coarseness of the sediments (conglomerates) 

 southward in the Narragansett area (toward Newport) and eastward in 

 the Boston area shows a derivation of the material from the east and' 

 south, or in general from a land to the southeast, pointing to steep stream, 

 gradients in that direction sloping northwestward fron; highlands beyond 

 but near the present border of the Atlantic coast. Thus the eastern limit 

 of the Acadian structure (New England States and the Maritime Prov- 

 inces of Canada) is not shown in southeastern Massachusetts. What the 

 direction of overturning is in that lost land off the present coast (Schu- 

 chert's Novascotica) is not directly known. 



LO^T LAND OFF THE COAST 



The conglomerates of Pennsylvanian age in the southern parts of the 

 Xarragansett area contain pebbles of quartzite or sandstone with an. 



