from the Lithographic Slate of Solenhofen. 367 
mens upon which they are founded do not belong to birds, or 
the formation, if it contained actual remains of birds, has been 
represented as more ancient than it really was. This applies 
even to the Glarus slates, which were regarded as Cretaceous at 
the period when a bird occurred in them, whilst they are only 
Tertiary. In my investigations of this bird (Palzontogr. iv. 
p- 90), I have repeatedly indicated that the phenomenon known 
under the name of Ornithichnites, attributed to the footprints, 
traces, or tracks of birds, is but little fitted to decide so important 
a matter as the antiquity of existence of an entire class of ani- 
mals. It has been made use of to claim a high antiquity for 
birds. But Ichnology, or the whole theory of fossil footprints, 
reposes only upon phenomena of resemblance; and although 
philosophers of the highest rank are to be found among its 
defenders, and its literature has acquired great dimensions, it is 
still destitute of a scientific foundation. 
Remains of birds have frequently been supposed to occur in 
the Lithographic Slate ; but it appeared, upon closer investiga- 
tion, that these were derived from Pterodactyles, or from the 
Rhamphorhynchi, which belong to the same group, from the 
structure of which we cannot well conclude that the animals 
were clothed with feathers ; and no traces of feathers were ever 
discovered with the numerous Pterodactyles found, of some of 
which the skeletons were perfect. (See my work ‘ Reptilien aus 
dem lithographischen Schiefer,’ 1860, p. 21.) 
From the circumstance that remains of birds were not to be 
found im pre-Tertiary formations, and that birds only begin to 
appear after the extinction of the Pterodactyles, which continued 
to occur up to the Chalk, it has been concluded that the Ptero- 
dactyle as it were represents the prototype of the bird. 
This rendered it the more surprising that recently a feather 
should be brought to light, and indeed precisely in the same 
formation, and even at the same spot, which furnishes the 
greatest number of Pterodactyles. This discovery is an event 
of so much importance in paleontology that it calls for the most 
thorough investigation. Although I had not the least reason to 
doubt of the integrity of the source through which the fossil was 
intrusted to me, still I must admit that it was not without some 
mistrust that I set about the examination of the subject, which 
had to be carried out in all directions, and in which the chief 
object was to answer the following three questions :— 
1. Is the rock the Lithographic Slate of the Upper Jurassic 
series ? 
2. Is the object upon it a feather such as birds possess ? 
3. Is the object really petrified, 7. e. of the same age as the 
fossils of the Lithographic Slate ? 
