I'ltlXDiriS AND BLASTOIDK. 157 



CRINOIDS AND BLASTOIDS. 



Quite a number of Oinoids and Blastoids, witli one or two 

 exceptions representing new species, have been recently dis- 

 covered at Le Grand on the Chicago and Northwestern Railroad . 

 a few miles east of Marshalltown, in Marshall county. Iowa. 

 The quarries at that locality have been in operation for many 

 years, yielding- a most excellent limestone, in part oolitic.* 



The exposure at Le Grand embraces about fifty feet of verti- 

 cal thickness. The base of the quarries consists of a fine-grained 

 blue sandstone, which has been used for curbing. This is suc- 

 ceeded by about 18 feet of heavy bedded, whitish grey oolitic 

 limestone, containing many shells and remains of fishes. Above 

 this is a succession of limestone beds of about 35 feet total 

 thickness. The lower part is subcrystalline, bedded in layers of 

 moderate thickness. It is succeeded by a fine-grained, brownish 

 or buff magnesian limestone, which at first is somewhat irregu- 

 larly bedded in rather thin strata, but toward the top occurs 

 in massive layers from 2 to 4 feet thick. Below the heavy beds 

 there are several thin layers of soft, sandy limestone, and these 

 contain the remains of Crinoids in remarkably fine preservation, 

 as the specimens herewith illustrated abundantly show, and 

 they occur in large quantities. 



*The oolitic layers, which are easily cut and polished, have been used ox ensively 

 for ornamental work and heavy masonry. The stone has proved to be a good building 

 material, and its dut ability is said to be well established by tests of many years. It has 

 outlived the prejudice which arose against it when first brought into use, based upon 

 the tendency of oolite in some other localities to crumble, a fault from which the Le 

 Grand rock appears to be free. 



