Algae, as Geological Guides. — fumes. 101 
proper, but in the opinion of the authors who have proposed them, they 
designate especially species of the Flysch, the identity of structure of 
which with the Jurassic forms that we here describe is far from being 
proved; this identity, at all events, is doubtful, on account of the dis- 
tance that separates the two epochs, a fact the more curious that it has 
been wished to be verified. Many types of Alga?, anterior to the species 
composing the group of Chondrites seoparius show among themselves 
analogies very close to Taonurus of the Flysch; every one of them is, 
however, distinguished by a particular generic name. The resemblance 
of these successive forms, constructed more or less upon the same plan, 
compels us to admit the existence of a great family, now entirely ex- 
tinct, that from Palaeozoic time to the Miocene, has not ceased to have 
some representative in the seas of our hemisphere." 
The contrast between these remarks by an author who would 
have a new genus for each successive geological horizon and 
a new species on almost every turn of the fossil form, with 
those of Lesquereux, who was also quite prone to make new 
species, is striking. In respect to the genus Taonurus he 
says :* 
"All the forms of Taonurus, considered as specifically different, may 
perhaps be modifications or varieties of one. They are rarely found in 
a good state of preservation and are difficult to study.'' 
The erroneous deductions which have been made upon the 
remains of pseudo-algse, as they are here considered, might be 
greatly multiplied. It is not, however, necessary to do this 
now. The following conclusions, we believe, may be fairly 
drawn from what has been given above : 
(1) The presumptive evidence of the presence of Algae in 
early geological time is good, but there is not good evidence 
that the greater number of species described as Algae are 
really such ; and any deductions based upon the number of 
genera and species recorded by authors are defective. (2) 
The great similarity of forms like Scolithus havinga very greal 
time range, is against their use as geological guides. ( X ) The 
poor state of preservation and the great variability they (ire- 
sent is also an argument unfavorable to their use. (4) Un- 
less the deductions made are corroborated by other evidence 
than that afforded by presumed fossil Algae, they can not be 
considered as having any great value. This other evidence 
must come from the presence of undoubted organized forms, 
or from-stratigraphieal evidence which can not lu- gainsaid. 
*Coal Flora. 2d Geol. Sur. Penn., P, vol. i, 1880, p. 9. 
