340 PRE-CAMBRIAN VOLCANIC BOMBS 



others, an original shape more nearly spherical. The crushing 

 it was subjected to, would appear to have taken place when the 

 interior was still in a semi-plastic state and the crust alone was 

 broken into irregularly shaped plates, thf^ edges of which were 

 more or less displaced. The distortion of form which the balls 

 suffered on impact varied in degree with their size and plasticity. 

 Some retained their form unaltered when they dropped to 

 earth, others appear to have had an exterior sufficiently viscid 

 at the moment of contact to coalesce, while yet others suffered 

 deformation without cohesion, or had their crust fractured, 

 while the displaced pieces were held together by the pasty 

 condition of the interior. While I have said the external sur- 

 face of the balls is smooth, this statement requires qualification, 

 as parts have a rough or broken appearance where they have 

 been in contact with others. A few show wher • a spherulitic 

 structure with fibrous radiations has been developed, a form 

 recognized as incipient of crystallization in igneous rocVs of 

 the more acid constituents. There was also to be seen on one 

 or two specimens a faint trace of venation somewhat similai- in 

 character, and this feature has also been detected on the ridges 

 of flow structure with the associated ash bed. Contact pro- 

 bably gave to the surface of the softer balls a cup-shaped 

 depression, or flattened or simply depressed it, the ultnnate 

 form retained by the balls doubtless being determined bj'- the 

 relative hardness of the impinging bodies. Some of the forms 

 found were oblong with rounded ends and somewhat constricted 

 in the middle ; they had a dumbell-like appearance fitting into 

 the inequalities of one another with, in many cases, such slight 

 adhesion that at a light tap of the hammer a group of them 

 would fall apart. 



Of the largest a fragment has been put in the Provincial 

 Museum It presents a curiously pitted appearance all over its 

 surface, giving to the plates, into which the crust is cracked, a 

 likeness to the scutes of ganoid fishes ; and taken alone it 

 might be supposed to be part of a fossil. 



