B. Smth—Ball or Pillow-form Rocks. 149 
apparently quite undisturbed, whilst others (Fig. 3) have ball structures 
strongly developed and exposed chiefly, be it noted, on their under 
surfaces. Where these surfaces curve upwards until they are nearly, 
or more than, at right angles to the normal plane of stratification, 
the sandstone laminz curve upwards and over, in conformity with 
them. In one or two places shales are plastered against the curved 
surfaces as if squeezed into spaces between the spheroids. 
a 
SE ee a Zz 
YN gl 
Fic. 3.—Ball structures in sandstone, Llwyn Bryn 
Dinas Wood, Llangedwyn. 
This example seemed to furnish conclusive evidence in favour of the 
balls or spheroids being due to internal concentric lamination, yet the 
next time I came across semi-spheroidal masses their curved surfaces 
tre +--> 
Ll | 
q--s--+~--- A 
N oa 
3.8. 
Fie. 4.—Sandstone ‘ ball’, Tyddyn-main, 
Llansilin. 
were due, quite as conclusively, to jointing and weathering. How- 
ever, many cases of the real thing were quickly forthcoming, and 
T have since found that true ball structures are quite as common as, 
if not more common than, the rounded masses due to shelling. 
