236 
ORIGIN OF LIFE IN AMERICA 
than they are now, hardly seems well founded. Another still 
stronger objection to Dr. Wallace’s * theory is that the 
northern forms alluded to as occurring in Chile and Patagonia 
belong almost all to different species, sometimes even to dif¬ 
ferent genera, from their northern relations. If storms had 
anything to do with this distribution they could only have 
acted during very long intervals of time so as to produce such 
specific and generic differences. Moreover, how could winds 
or storms affect the distribution of Carabus, which is a flight¬ 
less ground insect living under stones ? How could these 
agencies have transported fresh-water species across the im¬ 
mense tropical area, for several Chilean fresh-water forms 
exhibit a similar northern affinity ? These are some of the 
problems that present themselves to us. There are numbers 
of others. Why should the family of tortoises, Dermate- 
mydidae, which is known to have inhabited the North 
American continent since Cretaceous times, have become ex¬ 
tinct there and be now confined to Central America ? 
The scarcity of land and fresh-water fossils in Central 
America obliges us to resort to zoogeography and to the meagre 
geological information we possess in elucidating these and 
other problems. Before dealing with the general faunistic 
features of Central America, a few remarks on some of the 
more important geological characters will be of interest. 
The long neck of Central America from the isthmus of 
Tehuantepec to Panama, which joins North and South 
America to one another, has a length of about one thousand 
five hundred miles. We are sometimes apt to forget that it 
does not lie in a north and south direction, but almost east and 
west. Nearer South America the neck of land starts in a 
due westerly direction and only gradually turns somewhat 
towards the north and finally north-westward. Very little of 
this immense stretch of land has as yet been geologically sur¬ 
veyed. Nevertheless, some valuable hints as to its geological 
history have been gathered. In his essay on the geology of 
the isthmus of Panama, Professor Hill f tells us that, pos¬ 
sibly before the vast accumulations of more modern igneous 
and sedimentary rocks of Tertiary and post-Tertiary age were 
* Wallace, A. R., “Distribution of Animals,” Vol. II., p. 45. 
t Hill, R. T., “ Geological History of Panama,” pp. 241—257. 
