178 



GEOLOGY OF THE NARRAGANSETT BASIN. 



above. At the eastern end of the syncline shown upon the map these beds 

 may be seen turning northward and westward, with cross bedding plainly 

 showing the original top of the strata. The use of cross bedding in deter- 

 mining the original position of strata depends upon the fact that where the 

 inclined "fore set" layers are somewhat eroded the succeeding layers rest 

 upon their truncated edges. The evidence thus derived from the cross 

 bedding confirms the view that these beds are on the northern side of an 

 anticline whose axis is shown in the Perrins cut. 



These beds immediately below the coarse conglomerate also exhibit 

 worm burrows, trails, and current marks (see PL IX), and, what is even 

 more remarkable for this basin, the imprint of raindrops on an ancient 

 beach or exposed flat. (See PL X.) 



Raindrop imprints. — The locality exhibiting raindrop imprints is about one-half 

 mile southwest of the crossroads at the canoe end of the Attleboro syncline, 



where the reddish micaceous 

 sandstones below the Dighton 

 conglomerate are exposed in a 

 quarry. The surface of one 

 layer is current-marked, with 

 the steep fronts of the irregu- 

 lar ridges facing southeast 

 when oriented with reference 

 to the horizontal position, the 

 beds now standing vertical at this locality. Over the current marks are 

 the imprints of raindrops. These records of former meteorological condi- 

 tions are oh the northern and upper face of the vertical bed, and the 

 stratum is on the south side of the axis of the syncline, a position in every 

 respect consistent with the interpretation of the stratigraphic succession 

 advocated in this report. This is, so far as I am aware, the only locality 

 in the basin in which raindrop imprints may be seen in situ. The preserva- 

 tion of the record at tins locality, where the beds have been pushed up into 

 a vertical attitude, indicates that at least locally the dynamic metamorphism 

 in the Rhode Island coal field has not gone so far as has been commonly 

 believed. The condition of the imprints in this case further shows that in 

 the folding of the strata there was, at least on this hoiizon, little or no wide- 

 spread shearing of layer over layer, an action which in other localities is 



Fig. 25. — Diagram showing cross bedding. A, B, successively deposited 

 layers of cross bedding, or l 'ibre-set" layers; C, later layers, covering 

 the eroded surface of A, B ; o, a, a, a, erosion surfaces. 



