Templates declarations in header files?

Is it legal to have only a template declaration in a header file if the template is defined somewhere in a regular file?  That is,

For example, can I just include the header file "SomeClass.h" into the "SomeProgram.cpp" as long as the file "SomeClass.cpp" is compiled and linked into the program (but not included into "SomeProgram.cpp").  

****************SomeClass.h**************
template <class T> class SomeClass
{
public:
   int x;
   SomeClass(int i);  // Declared, not defined.
};
****************SomeClass.cpp**************
// Define constructor.
template <class T> SomeClass::SomeClass(int i);
{
  x = i;
}
****************SomeProgram.cpp**************
#include "someclass.h"
  SomeClass SC(5);

A EE client was trying to do this in a program and I didn't think it was allowed,  I just want to make sure.  It caused linker errors, which seems to make sense as things compiled, but the necessary functions weren't there.