P ALTEON TOLOG V. 5 



the absence of certain layers, or through the intercalation of new 

 ones not observ^ed in other localities under comparison. In the 

 fossils we have always an infallible guide, in cases where lithologi- 

 cal and stratigraphical characters would leave us in an inextricable 

 perplexity, regarding the position of certain strata. 



The value of palaeontology, as fundamental to all our geologi- 

 cal knowledge, is at present generally understood. Such of the 

 States as have instituted a geological survey of their territory 

 have shown their appreciation of its importance by making liberal 

 provisions by law for a careful collection of fossils, and for the sub- 

 sequent description and delineation in their report of all new and 

 interesting forms. 



During the progress of the geological survey of Michigan, a rich 

 harvest of fossils has been made, the class of corals in particular 

 being well represented in the collections. Our law provides that 

 due attention shall be paid to the description and figuring of new or 

 imperfectly known specimens. The number falling within this cat- 

 egory is so great that the limited compass allowed for the present 

 report will not admit of their being all described. 



Being compelled, therefore, to make a selection out of the mass of 

 material, I proposed to the Geological Board to give a more elab- 

 orate treatise on the indigenous fossil corals, omitting all descrip- 

 tion of mollusks and other fossil remains treated of and so amply 

 illustrated in the repjorts of other States, while the corals have re- 

 ceived comparatively little attention, notwithstanding that they be- 

 long to the forms most significant of the age of strata. The Board 

 consented to this plan, and I hope the general reader as well as 

 the scientist will not be displeased at being offered a carefully 

 elaborated monograph of this class, instead of a superficial descrip- 

 tion of a great variety of species from all classes. These were the 

 alternatives, as the fixed limits of the volume, as already stated, 

 would not permit my entering upon a critical examination of the 

 whole field of palaeontology. 



The species descriptions are illustrated by photographic figures, 

 printed by the new Albertotype process. The figures are necessa- 

 rily somewhat imperfect, because their convexity would not allow 

 their entire surface to be within the proper focus of the instrument. 

 Their absolute correctness in other respects, however, compensates 

 fully for these unavoidable imperfections. 



