370 GEOLOGY OF EASTERN WISCONSIN. 



abundance and variety, among which the crinoid family attained un. 

 nsual prominence; (3) that over areas of submarine sand-flats there 

 either V7as little life present, or, from the porous nature of the rock, it 

 has been illy preserved, and (4) that over the deeper areas, that de- 

 posited fine calcareous mud, the gigantic Cephalopods held sway. 

 The counterpart of all this is to be found among the coral reefs of to- 

 day. Vivid descriptions, almost specifically applicable to the forma- 

 tions in question, save in the modern aspect of the life, may be found 

 in the writings of Prof. Dana and Mr. Darwin on recent coral forma- 

 tions. A few quotations from the excellent work of the former on 

 Corals and Coral Islands, may find a place here by way of illustration 

 and confirmation. 



" Generally the barren areas much exceed those flourishing with zoophytes, and not 

 unfrequently the clusters are scattered hke tufts of vegetation in a sandy plain. The 

 growing corals extend up the sloping edge of the reef, nearly to low tide level. For ton 

 to twenty yards from the margin, the reef is usually very cavernous, or pierced with 

 holes or sinuous recesses, a hiding place for crabs and shrimps, or a retreat for the echini, 

 asterias, sea-anemones and moUusks; and over this portion of the platform the gigantic 

 Tridacna, sometimes over two feet long and five hundred pounds in weight, is often 

 found, lying more than half buried in the soKd rock, with barely room to gape a little 

 its ponderous shell, and expose to the waters a gorgeously colored mantle. Further in 

 are occasional pools and basins, ahve with all that Kves in these strange coral seas. 

 The reef rock, when broken, shows commonly its detritus origin. Parts are of compact, 

 homogeneous texture, and sohd white hmestone, without a piece of coral distinguishable, 

 and rarely an imbedded shell. But generally the rock is a breccia, or conglomerate, 

 made up of corals cemented into a compact mass, and- the fragments of which it con- 

 sists are sometimes many cubic feet in size." "Besides corals, the shells of the seas con- 

 tribute to it, and it sometimes contains them as fossils, along with bones of fishes, 

 exuvia of crabs, spines, and fragments of Echini, Orbitolites (disk-shaped foramunfers), 

 and other remains of organic hfe inhabiting reef grounds." 



Speaking of the masses of coral rock thrown upon the beach by the 

 waves, he says: 



" On moving these masses, which usually rest upon then- projecting angles, and have 

 an open space beneath, the waters at once became ahve with shrimps, crabs and fish, 

 escaping from their disturbed shelter; and beneath appear various Actinise, or living 

 flowers, the spiny echini, and sluggish biche-de-mar, while swanns of shells, having each 

 a soldier crab for their tenant, walk ott with unusual Hfe and stateliness. Moreover, 

 dehcate corallines, Ascidiee and sponges tint with lively shades of red, green and pink, 

 the under surface of the block of coral which had formed the roof of the little grotto." 



In other portions of the same work, there are frequent descriptions 

 or references to sandrock, solid limestone, and various conglomeritic 

 forms, that might almost have been embodied as a portion of the lith- 

 ologic.ll description of this exposure of the Eacine limestone. It does 

 not appear, however, that Corals played so conspicuous a part, relat- 



