How to select a value depending on 2 attributes from separate nodes using XPath in C#?

So, I have an XML file like the following structure,

<Root>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-01-31</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>-4.58849</GrandChild1>
      <GrandChild2>288</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-02-28</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>4.58015</GrandChild1>
      <GrandChild2>284</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="1">
    <Child1>2014-03-31</Child1>
    <Child2 TimePeriod="M4">
      <GrandChild1>-0.65693</GrandChild1>
      <GrandChild2>284</GrandChild2>
    </Child2>
  </Parent>
  <Parent StoreDate="2014-12-31" Type="3">
    <Child1>2014-03-31</Child1>
    <Child2 TimePeriod="M1">
      <GrandChild1>-5.65693</GrandChild1>
      <GrandChild2>2334</GrandChild2>
    </Child2>
  </Parent>
</Root>

I want to select all , if attribute [@Type] of is 1 and attribute [@TimePeriod] of is M1.

I've loaded in an XElement names xElement. Then, I'm using

IEnumerable<XElement> elements = xElement.XPathSelectElements("(/Parent[@Type='1'] | /Parent[Child2/@TimePeriod='M1'])/Child2/GrandChild1");

This supposed to select only the 1st and 2nd from the above XML file. Instead it is selecting all . What am I doing wrong?

I've tried using 'and' instead of '|' in the code. But it's not working at all and throwing exception.

Any suggestions guys? Thanks in advance.