lufiforial Com nit'iit. o8t) 
rectiou and feldspar in another, the hitter takhiji' radiated and 
branching forms under varying tension and viscosity in tiie niag- 
matic mass. As the colloiihd substance is further separated, the 
specialized growtlis go on y*a// jk(sii, resulting in concentric zonal 
structures or in radiated sphernlites. or im]>erfect arliorescent 
forms — and sometimes in holocrystalline sphernlites. 
It is difficult to see, from the discussion, wherein Mr. Cross 
finds warrant for the existence of this supposed anterior, globular 
■colloidal substance, or wherein his hyi)othesis enlightens or even 
embraces -'the conditions favondile to or causing spherulitic 
growths, "' (p. 4;)0) wliich h(> announces as its purpose. In fact 
it appears, from the statements of ^Ir. Cross, that the general 
magma, after the primary segregation of the phenocrysts of plag- 
ioclase, biotite, microlites of augite and grains of magnetite, had 
nothing left but the same elements that he deems characteristic of 
this colloidal sul)stance, and it is i)erhaj)s reasonable to suppose 
the magma itself, en nKotsr at this time was colloidal aud gener- 
iited the sphernlites in the same manner as supposed for the iso- 
lated colloidal glo])ules. it is only by assuming the minute pri 
mar}" globules of the magma itself as it existed just prior to the 
«pherulite-forniing stage, as the initial colloidal glo1)ules, that 
there can l)e. so far as we can see, any warrant for the hypothe- 
sis, and if the hypothesis be reduced to this, il is no hy})othesis 
at all. for it only assumes a well-known condition of amorphous 
matter. ^Ir. Cross's discriptions are clear and comprehensible, 
and the pa})er. aside from its philosojdiy. is a vaiualilc contrilm- 
tion to American petrography. 
The paper of jNIr. Iddings treats of a stage in spheruliti/.atiou 
subseciuent to that above described, viz. : the process of forma- 
tion of the crystalline inter-growths and the cliaractersof thecrvs- 
tals formeci. It is based on a study of a new series of thin sec- 
tions of the litlu^idite of Obsidian Clitf. in Yellowstone Park, the 
sections presenting 2(> examples of one phase of the rock. Tlie 
new study in Mi'. Iddings" opinion corroborates, and also extends 
the conchisions reached l>y the former research, adding three new 
minerals, tininnaline, mica and zircon, to this rock. Mr. Iddings 
likewise rejects, as he before ignored, the term " microfelsite, " 
and Itelieves it is demonstrable that even the finest of the sphern- 
lites are l)nt very small forms of largei" oiu's wliose structure and 
composition can be observed. 
