Association of American Geologists and Naturalists. 351 
Geographical distribution.—From the extensive destruction of these 
animals, and the transportation of their broken remains over large 
areas, it is impossible to determine what has been their original extent 
when living. The fragments have doubtless been often drifted to great 
distances from their original places of growth. Wherever they are 
‘known to exist in any degree of perfection, their geographical extent 
is very limited. Of the nine or ten species known in the Niagara 
group, not more than one is known to range beyond a distance of forty 
or fifty miles, and this one not more than sixty or seventy. Nearly all 
of them are confined to the space of a few miles. Certain situations 
appear to have been favorable to their growth, and though the nature 
of the deposit may appear equally uniform for a much greater distance, 
they do not occur. 
In the limestones of the Helderberg series, their remains are widely 
distributed, but from their being usually in fragments, the fact furnishes 
ho argument that they were thus widely distributed when living. - In 
most cases in this series and in the Hamilton group, the perfect speci- 
mens are scarcely known beyond the single locality. 
In the Portage group, the only perfect species known does not extend 
horizontally more than ten or twelve feet, and the place appears as if a 
forest of these beautiful forms had been swept down and covered with 
the soft mud above. fs ’ 
_ The well ascertained species of the Chemung group, are almost equal- 
ly limited in their geographical range. _ oft pees 
_ From all the facts collected it appears, that certain epecies) though 
preéminently typical of certain formations, cannot be relied ae OFer 
any wide area of country. Their presence may be relied upon as iden- 
tifying certain formations, and their absence is not by any means to In- 
terfere with conclusions regarding identity drawn from other sources. 
The natural history of this class of animals, in connection with their 
geological distribution, is exceedingly curious and interesting, and these 
few facts may serve to enlist observation upon their situation and con- 
dition in other parts of the country. ere 
‘Dr. Owen read a paper ona universal system of geological 
coloring and symbols. sh DF : 7 
» -It was proposed that the three primitive colors should be adopted to 
represent the three, great paleontological periods, viz. blue (indigo) 
for the primary fossiliferous ; red (light red, or a carmine tint) for the 
secondary ; yellow (zamboge) for the tertiary, —that the principal groups 
of these periods, when compatible with distinctness, be indicated by a 
variation in the tint, the intensity increasing in the descending order, 
and, if necessary, imparting at the same time to the limestones a bluish 
cast, and to the argillace deposits a greyish tint. 
