THE FLORISSANT SHALES OF COLORADO l6l 



in many respects very unlike that of the past. In the Themigra- 

 shale are remains of redwood trees ; and there are even extermina- 

 great redwood trunks, now completely silicified, stand- tlon of 

 ing at Florissant. Today the redwood, once widely 

 spread over the northern hemisphere, is making its 

 last stand, confined to a rather small area in California. 

 In the shale is also the Ailanthus or Tree of Heaven, 

 a genus now confined to eastern Asia. We find in addi- 

 tion leaves of magnolia, elm, beech, chestnut, poplars, 

 pines, and oaks, - - such an assemblage as does not exist 

 in the Rocky Mountains today. We are reminded 

 rather of the mixed hardwood forests of the Eastern and 

 Southern states. We wonder why some of these trees 

 have disappeared from Colorado ; why there are no 

 longer any elms or chestnuts native in the region, though 

 they still exist in the Eastern states. Was it the change 

 of climate, or did some blight sweep them off, like the 

 chestnut blight which is now so destructive along the 

 Atlantic seaboard ? There were figs and walnuts, - 

 we have fruit of both ; wine grapes and holly, roses of 

 four different kinds, and many other plants dear to the 

 eye or lips of man ; but there were no men to see or use 

 them. These things must seem strange to those who 

 imagine that the beauty and wealth of nature exists for 

 us alone ! 



5. In Africa are found certain blood-sucking flies The fossil 

 which carry the parasites of disease to men and animals. 

 These are the tsetse flies (Glossina), and one of them is 

 the bearer of the cause of sleeping sickness, which has 

 wiped whole villages of people off the map. Another 

 makes it almost impossible to keep cattle in certain 

 localities. Many remarkable animals which once 

 lived in North America are now extinct, and it is often 

 very difficult to imagine the cause of their disappear- 



