FOSSILS. 



271 



FIG. 171. 



Maclurea matutina. 



The genus maclurea is not found higher than the Trenton limestone, and is therefore characteristic of 

 the lowest beds of the lower siluriau. It is a nucleobranchiate mollusk, and is most nearly allied to the 

 family Atlantidae. The following is Woodward's description of the 

 genus. " Shell discoidal, few whorled, reversed (the apical whorls 

 being brought down to the base and the umbilicous flattened out) 

 upper surface convex, deeply perforated instead of raised into a spire ; 

 outer side spirally grooved ; operculum sinistrally sub-spiral, solid, with 

 two internal projections for the attachment of muscles one of them 

 beneath the nucleus, and very thick and rugose." 



Both species of the Maclurea in the calciferous sandrock are obscure, 

 as they appear in Vermont, both from weathering and the rough nature 

 of the matrix. Fig. 171 represents the Maclurea matutina, the more 

 common form. This species is discoidal, involute ; the spire is not 

 elevated; the umbilicus is deep, and the surface is not certainly known; 

 probably it is striated. 



The Maclurea sordida has a discoidal shell ; its spire is not elevated; 

 the mouth is slightly expanded, and the surface is apparently smooth. 

 The first of these species occurs at the east part of Snake Mountain in 

 Addison, near Orwell Center, in Benson and West Haven. The other species probably occurs in 

 connection with the preceding in several of these localities; but we found it best shown in a bowlder picked 

 up in Pawlet, which had been transported several miles from its original position. 



Ophileta. Observers have found species of this genus in Vermont, probably the 0. levata Van. The 

 generic (or sub-generic) character of Ophileta is the following : Discoidal; spire sunk above ; umbilicus 

 below perfectly open, and exposing the whorls all on one plane; whorls numerous; truncate and triangular 

 exteriorly; mouth trigonal. Forms with deeply concave spires. The best authorities consider this sub- 

 genus as related to the beautiful living genus Janthina. 



Geological Position and Equivalency. 



All agree that the calciferous sandrock is at or near the base of the lower silurian, 

 certainly the particular terrain which has just been described. But some geologists 

 suppose that the red sandrock series is the same as the calciferous sandrock, and perhaps 

 including the Potsdam sandstone. We give elsewhere our views upon this subject ; and 

 will simply say here that in case of the reference of the red sandrock series to the lower 

 silurian, the conjectural range of calciferous sandrock in Shoreham and Orwell, already 

 described, with the accompanying conjectural Potsdam sandstone, is a part of the range of 

 red sandrock, though different to an external view. It is just such a change as metamor- 

 phism might produce. 



We will mention a few localities of rocks which are represented as red sandrock upon 

 the map, but which are the same rock as the exposure at Newell's Mill in Shoreham. At 

 Mr. De Long's house in the northeast part of Shoreham, there arc exposures of limestone 

 with a strike of N. 10-20 E. and dipping 4o-72 W. This position is unusual, and is 

 probably local. At Lemonfair River, a short distance west of the foregoing, is a precipi- 

 tous ledge of a calciferous sandstone dipping 2 E. At Birchard's Sawmill still further 

 west, the rock runs N. 10 E, and dips 15 E. In the northeast corner of Shoreham, 

 there are three systems of joints in these rocks. N. 45 E., dip 65 E ; N. 65 W., per- 

 pendicular ; and N. 45 W., dip 75 W. 



