lJ6Jr Professor Mulder 



are indeed authors wlio think, that the Upper Silurian is so linked 

 on to the Devonian, that the former, or a large portion of it, might 

 advantageously be merged in the latter ; and if their views prevailed, 

 the only portion of my system or terrain which Professor Sedgwick's 

 proposition leaves to me would also be swallowed up, and thus, by 

 invasions on both sides, the poor Silurian system would be obliterated. 



On the principle, however, of strata identijied by their fossils^ geo- 

 logists, I hope, agree with me to the conviction in which I abide, that 

 in whatever rocks, and to whatever depths the Lower Silurian types 

 extend, the tracts so characterised must be considered to belong to 

 the " Silurian System." 



In contending for the preservation of that system in its unity, I 

 in no way detract from the very great merit of the researches of my 

 friend, Professor Sedgwick, in developing the physical structure, dis- 

 locations, slaty impress, fossil characters, and other phenomena of 

 the rocks of North Wales, Cumberland, and Westmoreland. 



As already stated, I formerly hoped he would also point out in 

 their lowest division the existence of a distinct zoological type which 

 would have entitled those rocks to a separate name ; but having 

 failed to do so, it seems to me manifest, that his " Cambrian" cannot 

 now be sustained by dismembering a fossiliferous system which has 

 been so long established, so largely developed, and so widely applied 

 over the world as the Silurian. AVhether geologists will use the word 

 *' Cambrian," in reference to still older and often unconformable 

 greywacke lying beneath all the beds with Silurian fossils, it is not 

 for me to determine. My chief object in this communication is to 

 explain how, by the progress of research, the protozoic types of 

 various parts of Northern Europe, including North Wales, have been 

 shewn to be true equivalents of the lower part of a natural system 

 which I proposed twelve years ago, and which geologists of various 

 countries adopted after a careful scrutiny of the evidences on which 

 jt was established. 



On the Protein Question. By Pi*ofessor MuLDER of Utrecht. 

 Communicated by Professor J. F. W. Johnston. 



Durham, llth June 1847. 



My Dear Sir, — Will you favour me by inserting In your ensuing 

 number, the following additional communication from Professor 

 Mulder on the Protein question ? The perusal of it will shew you 

 that we arc slowly progressing towards a more perfect knowledge of 

 this important substance. 



The state of our knowledge in regard to it is at present nearly as 

 follows : — 



1. There exists in the parts of animals and plants a substance to 



