298 THOMAS L. WATSON 



in Fig. 2, the spheroidal growths compose by far the bulk of the 

 rock. Variation of the nodules is from nearly perfect spheres to 

 ellipsoidal in shape, and in size they range from a fraction of an 

 inch to several inches across. They can readily be broken out of 

 the rock in complete form, almost or entirely free from the inclosing 

 matrix. Compression due to flow movements in the rock while 

 still plastic is but slightly indicated in the shapes of the nodules. 



The nodules are uniformly greenish black in color, composed, as 

 a rule, almost or entirely of dark ferromagnesian minerals, which 

 show a radial arrangement about a common center. They are 

 usually crowded close together, touching each other in many cases, 

 with the interspaces largely filled with clear white cleavable and 

 lustrous feldspar, a very little quartz, and penetrating laths of horn- 

 blende. Relatively large and small perfect crystals of reddish- 

 brown titanite are very generally distributed through the rock, 

 common to both nodules and matrix. In some instances feldspar 

 and quartz, rarely pyrite, in small grains, have been observed, each 

 in different spheroids, to form a nucleus about which the somewhat 

 fibrous ferromagnesian minerals have arranged themselves in a 

 radial structure. Both the feldspar and the quartz may occur 

 together, forming the nucleus of a single nodule. Of the nucleal 

 minerals feldspar is perhaps the most common. In a majority of 

 the spheroids, however, the nucleus or core of feldspar and quartz 

 practically fails, when the nodules become spheres of ferromagnesian 

 minerals. 



Search through the literature develops, from descriptions of 

 orbicular structure in deep-seated rocks, several important differ- 

 ences in structure and composition of the spheroids in the Carolina 

 rock from those usually observed in similar rocks from other localities. 

 The chief differences to be noted are : (i) In the Carolina rock the sphe- 

 roids are marked by the almost entire absence of concentric structure, 

 which ordinarily characterizes the nodules of deep-seated orbicular 

 rocks described from other localities. Only the barest semblance 

 of such structure is noted in the Carolina rock, and it entirely fails 

 in most of the spheroids. (2) The spheroids of orbicular rocks 

 hitherto described are composed of several minerals, usually the 

 principal constituents of the groundmass, though additional ones 



