12 THE COLLECTION OF FOSSIL VERTEBRATES 
broad shallow valleys in the chalk and shale. In the dry climate 
The Find Of the present day the sides of these valleys often are 
ingand _ bare rock, carved by wind and the infrequent storm- 
Collecting bursts of rain into the fantastic maze of cliffs and 
ot ieee: winding canons known as “bad-lands.”’ Here and 
there, projecting from an outstanding ledge or trailing in frag- 
ments down some crumbling slope, a fossil bone may be seen by 
the trained eye of the collector as he searches along the rock 
exposures; and quarrying in around the bone he is sometimes 
rewarded by a skull, sometimes by a string of vertebrz, occa- 
sionally by a whole skeleton, buried in the rock except for such 
parts of it as have been weathered out and washed away. 
To excavate the fossil without damaging the brittle bones, 
buried as they are in a weak and shattered mass of heavy shale 
or chalk, is a slow and delicate operation, requiring special 
methods and considerable care and skill. Then the specimen 
must be packed, and sent in to the Museum, where the rock is 
removed and the specimen is prepared for exhibition. When the 
bones are as much crushed and distorted as those represented in 
the photograph (page 10) the matrix is removed from one side 
only, and the specimen is thus placed on exhibition. 
Temporarily placed in the bottom of the case is a large Ple- 
siosaur skeleton, only partly removed from the rock. This 
Important specimen unfortunately lacks the skull. Beside the 
Specimens |ower stairway is a Mosasaur skeleton, the finest speci- 
in Corridor. en of its kind ever found, and above it is a large fish 
skeleton which was found in the same strata in western Kansas. 
Beside the upper stairway are three skeletons of Ichthyosaurs, 
another long extinct group of marine reptiles, of fish-like appear- 
ance, paralleling the modern Whales among mammals. 
EAST WING. HALL NO. 406. FOSSIL MAMMALS. 
The ancestors of our modern quadrupeds are to be found in 
the East Wing, No. 406, together with many extinct races more 
Arrangement OF less nearly related to them. All the fossil speci- 
of the Fossil mens of each group of mammals are placed together 
Mammals. in one alcove, where they have been arranged ac- 
cording to their geological age. Thus all the fossil Horses, direct 
